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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_asio.history"></a><a class="link" href="history.html" title="Revision History">Revision History</a>
</h2></div></div></div>
<h4>
<a name="boost_asio.history.h0"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_36_0___boost_1_89"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_36_0___boost_1_89">Asio
      1.36.0 / Boost 1.89</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed an issue, introduced in Asio 1.35.0, that prevented the creation
          of internal threads required for running some asynchronous operations on
          a <code class="computeroutput"><span class="identifier">thread_pool</span></code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">co_spawn</span></code> to adhere
          to the asynchronous operation requirement for non-reentrant invocation
          of the completion handler.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="special">[[</span><span class="identifier">noreturn</span><span class="special">]]</span></code> attribute to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">throw_exception</span></code>.
        </li>
<li class="listitem">
          Fixed compilation errors in <code class="computeroutput"><span class="identifier">channel</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">(</span><span class="identifier">error_code</span><span class="special">)&gt;</span></code> and <code class="computeroutput"><span class="identifier">concurrent_channel</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">(</span><span class="identifier">error_code</span><span class="special">)&gt;</span></code>.
        </li>
<li class="listitem">
          Fixed a compilation issue with the Bullseye compiler.
        </li>
<li class="listitem">
          Fixed an <code class="computeroutput"><span class="identifier">awaitable</span></code> coroutine
          compile error with the clang shipped with MSVC.
        </li>
<li class="listitem">
          Fixed support for platforms that don't define <code class="computeroutput"><span class="identifier">SA_NOCLDWAIT</span></code>.
        </li>
<li class="listitem">
          Worked around a warning that occurs when building with <code class="computeroutput"><span class="identifier">_FORTIFY_SOURCE</span></code>
          on recent <code class="literal">g++</code>.
        </li>
<li class="listitem">
          Added a documentation note on <code class="computeroutput"><span class="identifier">basic_signal_set</span></code>
          async signal safety.
        </li>
<li class="listitem"><h4>
<a name="boost_asio.history.h1"></a>
          <span class="phrase"><a name="boost_asio.history.asio_1_35_0"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_35_0">Asio
          1.35.0</a>
        </h4></li>
<li class="listitem">
          Added allocator constructors to <code class="computeroutput"><span class="identifier">execution_context</span></code>,
          <code class="computeroutput"><span class="identifier">io_context</span></code> and <code class="computeroutput"><span class="identifier">thread_pool</span></code>. The supplied allocator is
          used for allocating objects associated with the execution context, such
          as services, the internal state for I/O objects like sockets or timers,
          and strands. The allocator may also be accessed by user code via the <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="identifier">allocator</span><span class="special">&lt;&gt;</span></code>
          class template.
        </li>
<li class="listitem">
          Extended the allocation example to cover <code class="computeroutput"><span class="identifier">execution_context</span></code>
          allocation.
        </li>
<li class="listitem">
          Added a new configuration parameter "timer" / "heap_reserve"
          that may be used to reserve space in the vector used for a timer queue's
          heap. This may be used to preallocate sufficient space such that the creation
          of new timers does not trigger further allocations.
        </li>
<li class="listitem">
          Added a new configuration parameter "resolver" / "threads"
          that is used to specify the number of internal threads used by <code class="computeroutput"><span class="identifier">async_resolve</span></code> to emulate asynchronous
          address resolution. If this is set to a non-zero value, that number of
          threads will be created when the first resolver object is constructed.
          Otherwise, it defaults to a single thread that is created on the first
          call to async_resolve.
        </li>
<li class="listitem">
          Removed <code class="computeroutput"><span class="identifier">deadline_timer</span></code>,
          <code class="computeroutput"><span class="identifier">basic_deadline_timer</span></code> and
          <code class="computeroutput"><span class="identifier">time_traits</span></code> from the convenience
          header <code class="literal">boost/asio.hpp</code>.
        </li>
<li class="listitem">
          Ensured that the Windows named pipes created by <code class="computeroutput"><span class="identifier">connect_pipe</span></code>
          use unique names that don't conflicting if Asio is used in multiple, independent
          plug-in DLLs.
        </li>
<li class="listitem">
          Changed <code class="computeroutput"><span class="identifier">BOOST_ASIO_CONCURRENCY_HINT_SAFE</span></code>
          to be consistent with the <code class="computeroutput"><span class="identifier">io_context</span></code>
          default constructor.
        </li>
<li class="listitem">
          Fixed the documentation for <code class="computeroutput"><span class="identifier">BOOST_ASIO_CONCURRENCY_HINT_UNSAFE_IO</span></code>
          to reflect that registration locking is still enabled.
        </li>
<li class="listitem">
          Added separate <code class="literal">b2</code> and <code class="literal">cmake</code> build
          targets for optional dependencies.
        </li>
<li class="listitem">
          Fixed a build error in the serialization example.
        </li>
<li class="listitem">
          Fixed some shadow variable warnings.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h2"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_34_2___boost_1_88"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_34_2___boost_1_88">Asio
      1.34.2 / Boost 1.88</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed an ambiguous overload issue that occurred when passing a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">span</span></code> to the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span></code>
          function.
        </li>
<li class="listitem">
          Added overview documentation on the available runtime configuration options.
        </li>
<li class="listitem">
          Updated the overview documentation to reflect the use of <code class="computeroutput"><span class="identifier">deferred</span></code> as the default completion token.
        </li>
<li class="listitem">
          Updated the <code class="computeroutput"><span class="identifier">async_result</span></code>
          documentation to reflect the current type requirements placed on specialisations
          of the trait.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h3"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_34_1"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_34_1">Asio
      1.34.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added <code class="computeroutput"><span class="keyword">noexcept</span></code> qualifiers
          to various <code class="computeroutput"><span class="identifier">local</span><span class="special">::</span><span class="identifier">basic_endpoint</span></code> member functions, to make
          it consistent with <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">basic_endpoint</span></code>.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">config</span></code> class's handling of integer values.
        </li>
<li class="listitem">
          Fixed a use-after-move error in <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">ranged_parallel_group</span></code>.
        </li>
<li class="listitem">
          Fixed an incorrect default template argument in the implementation of
          <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span></code>.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">io_uring</span></code> implementation
          so that it does not attempt to re-register internal descriptors with the
          reactor after a fork, if they were not previously registered.
        </li>
<li class="listitem">
          Fixed an uninitialised member in the <code class="computeroutput"><span class="identifier">thread_pool</span></code>
          default constructor.
        </li>
<li class="listitem">
          Removed some spurious macro definitions that were left after the removal
          of deprecated buffer functionality.
        </li>
<li class="listitem">
          Added documentation to clarify the use of <code class="computeroutput"><span class="identifier">file_base</span><span class="special">::</span><span class="identifier">flags</span></code>
          when opening a file.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h4"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_34_0___boost_1_87"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_34_0___boost_1_87">Asio
      1.34.0 / Boost 1.87</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Relaxed disposition requirements to require only nothrow move, rather than
          copy.
        </li>
<li class="listitem">
          Fixed compile error when threading support is disabled.
        </li>
<li class="listitem">
          Fixed compile error when <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING</span></code>
          is defined.
        </li>
<li class="listitem">
          Fixed compile error when using Clang 19.
        </li>
<li class="listitem">
          Changed <code class="computeroutput"><span class="identifier">thread_pool</span><span class="special">::</span><span class="identifier">join</span><span class="special">()</span></code>
          to ensure that it stops threads that are subsequently added to the pool
          using <code class="computeroutput"><span class="identifier">thread_pool</span><span class="special">::</span><span class="identifier">attach</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Fixed the offsets passed to <code class="computeroutput"><span class="identifier">io_uring_prep_write_fixed</span></code>
          and <code class="computeroutput"><span class="identifier">io_uring_prep_read_fixed</span></code>,
          when they are used for stream-oriented operations.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h5"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_33_0"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_33_0">Asio
      1.33.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added support for using byte spans and sequences of byte spans as buffer
          sequences. This means that they can be passed directly to I/O operations
          such as <code class="computeroutput"><span class="identifier">async_read</span></code>.
        </li>
<li class="listitem">
          Added support for dispositions, which are types that can be used to test
          whether an asynchronous operation completed without error. This includes
          <code class="computeroutput"><span class="identifier">error_code</span></code> and <code class="computeroutput"><span class="identifier">exception_ptr</span></code>, but can be extended to
          user types via specialisation of the <code class="computeroutput"><span class="identifier">disposition_traits</span></code>
          class template. Generic code that is intended to work in terms of dispositions
          should not use <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">disposition_traits</span></code> directly, but instead:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Test whether a disposition holds no error by comparing against <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">no_error</span></code> (of type <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">no_error_t</span></code>).
              </li>
<li class="listitem">
                Use <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">to_exception_ptr</span></code> to convert a disposition
                to a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span></code>.
              </li>
<li class="listitem">
                Use <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">throw_exception</span></code> to throw an exception
                that corresponds to the disposition, after first testing the disposition
                against <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">no_error</span></code>.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added disposition support to the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span></code>
          completion token, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>-based coroutines, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">spawn</span><span class="special">()</span></code>,
          and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">cancellation_condition</span></code>.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="identifier">service_maker</span></code>
          abstract base class. A <code class="computeroutput"><span class="identifier">service_maker</span></code>
          is an object that is passed to an execution context's constructor, and
          allows services to be added at context construction time. Additional constructor
          overloads have been added to <code class="computeroutput"><span class="identifier">io_context</span></code>
          and <code class="computeroutput"><span class="identifier">thread_pool</span></code> that accept
          a <code class="computeroutput"><span class="identifier">service_maker</span></code>.
        </li>
<li class="listitem">
<p class="simpara">
          Added <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">config</span></code>. The <code class="computeroutput"><span class="identifier">config</span></code>
          class provides access to configuration parameters that are associated with
          an execution context. The class is intended for use by asio internals,
          or by libraries or user-provided abstractions that build on top of asio.
          These configuration parameters will typically be used to fine tune behaviour,
          such as enabling or disabling certain optimisations. When constructing
          an execution context, such as an <code class="computeroutput"><span class="identifier">io_context</span></code>,
          the caller may optionally pass a <code class="computeroutput"><span class="identifier">service_maker</span></code>
          to install a concrete configuration service into the context. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span> <span class="identifier">ctx</span><span class="special">{</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">config_from_env</span><span class="special">{}};</span>
</pre>
<p class="simpara">
          The configuration parameters' values are accessed using the <code class="computeroutput"><span class="identifier">config</span></code> class, passing a section, key
          and default value:<br>
        </p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">config</span> <span class="identifier">cfg</span><span class="special">{</span><span class="identifier">ctx</span><span class="special">};</span>
<span class="keyword">bool</span> <span class="identifier">enable_locking</span> <span class="special">=</span> <span class="identifier">cfg</span><span class="special">.</span><span class="identifier">get</span><span class="special">(</span><span class="string">"scheduler"</span><span class="special">,</span> <span class="string">"locking"</span><span class="special">,</span> <span class="keyword">true</span><span class="special">);</span>
</pre>
</li>
<li class="listitem">
          Added an initial set of configuration parameters recognised by asio's
          <code class="computeroutput"><span class="identifier">io_context</span></code> and <code class="computeroutput"><span class="identifier">thread_pool</span></code> implementations:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                "scheduler" / "concurrency_hint" (int, default
                <code class="computeroutput"><span class="number">0</span></code>) - A suggestion to
                the scheduler of how many active should be used for running completion
                handlers.
              </li>
<li class="listitem">
                "scheduler" / "locking" (bool, default <code class="computeroutput"><span class="keyword">true</span></code>) - May be set to <code class="computeroutput"><span class="keyword">false</span></code> to disable locking in the scheduler,
                in which case care must be taken not to perform concurrent operations
                on the execution context or its I/O objects.
              </li>
<li class="listitem">
                "scheduler" / "locking_spin_count" (int, default
                <code class="computeroutput"><span class="number">0</span></code>) - The number of times
                to first attempt to acquire the lock without blocking.
              </li>
<li class="listitem">
                "scheduler" / "task_usec" (long, default <code class="computeroutput"><span class="special">-</span><span class="number">1</span></code>)
                - The maximum time that the scheduler will wait for its reactor task
                to complete.
              </li>
<li class="listitem">
                "scheduler" / "wait_usec" (long, default <code class="computeroutput"><span class="special">-</span><span class="number">1</span></code>)
                - The maximum time that the scheduler will wait on its wakeup event
                in an idle thread.
              </li>
<li class="listitem">
                "reactor" / "preallocated_io_objects" (unsigned
                int, default <code class="computeroutput"><span class="number">0</span></code>) - The
                number of internal reactor I/O object states to allocate at construction.
              </li>
<li class="listitem">
                "reactor" / "registration_locking" (bool, default
                <code class="computeroutput"><span class="keyword">true</span></code>) - May be set to
                <code class="computeroutput"><span class="keyword">false</span></code> to disable locking
                in the reactor around I/O object registration, in which case care
                must be taken not to concurrently open or close I/O objects.
              </li>
<li class="listitem">
                "reactor" / "registration_locking_spin_count"
                (int, default <code class="computeroutput"><span class="number">0</span></code>) - The
                number of times to first attempt to acquire the lock without blocking.
              </li>
<li class="listitem">
                "reactor" / "io_locking" (bool, default <code class="computeroutput"><span class="keyword">true</span></code>) - May be set to <code class="computeroutput"><span class="keyword">false</span></code> to disable per I/O object locking
                in the reactor, in which case the execution context must be single-threaded
                and care must be taken not to perform concurrent calls to I/O operations'
                initiating functions.
              </li>
<li class="listitem">
                "reactor" / "io_locking_spin_count" (int, default
                <code class="computeroutput"><span class="number">0</span></code>) - The number of times
                to first attempt to acquire the lock without blocking.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Removed some previously deprecated facilities:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Removed Boost.Coroutine-based <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code> overloads. The <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code> function now works only with the
                fiber support in Boost.Context.
              </li>
<li class="listitem">
                Removed deprecated <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">connect</span></code>
                overloads.
              </li>
<li class="listitem">
                Removed deprecated <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v4</span></code>
                member functions.
              </li>
<li class="listitem">
                Removed deprecated <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v6</span></code>
                member functions.
              </li>
<li class="listitem">
                Removed deprecated constant <code class="computeroutput"><span class="identifier">socket_base</span><span class="special">::</span><span class="identifier">max_connections</span></code>.
              </li>
<li class="listitem">
                Removed deprecated classes <code class="computeroutput"><span class="identifier">const_buffers_1</span></code>
                and <code class="computeroutput"><span class="identifier">mutable_buffers_1</span></code>.
              </li>
<li class="listitem">
                Removed deprecated function <code class="computeroutput"><span class="identifier">buffer_cast</span></code>.
              </li>
<li class="listitem">
                Removed deprecated <code class="computeroutput"><span class="identifier">use_future_t</span><span class="special">::</span><span class="keyword">operator</span><span class="special">[]</span></code>.
              </li>
<li class="listitem">
                Removed deprecated alias <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">append</span></code>.
              </li>
<li class="listitem">
                Removed deprecated alias <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">prepend</span></code>.
              </li>
<li class="listitem">
                Removed deprecated alias <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">as_tuple</span></code>.
              </li>
<li class="listitem">
                Removed deprecated alias <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">deferred</span></code>.
              </li>
<li class="listitem">
                Removed deprecated class <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">rfc2818_verification</span></code>.
              </li>
<li class="listitem">
                Removed deprecated alias <code class="computeroutput"><span class="identifier">io_service</span></code>.
              </li>
<li class="listitem">
                Removed deprecated class <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">work</span></code>.
              </li>
<li class="listitem">
                Removed deprecated <code class="computeroutput"><span class="identifier">io_context</span></code>
                <span class="emphasis"><em>run functions</em></span>.
              </li>
<li class="listitem">
                Removed deprecated function <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">reset</span></code>.
              </li>
<li class="listitem">
                Removed deprecated <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">service</span></code>
                member functions.
              </li>
<li class="listitem">
                Removed deprecated <code class="computeroutput"><span class="identifier">dispatch</span></code>
                and <code class="computeroutput"><span class="identifier">post</span></code> members
                from <code class="computeroutput"><span class="identifier">io_context</span></code> andxi
                <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">strand</span></code>.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Deprecated <code class="computeroutput"><span class="identifier">basic_io_object</span></code>.
        </li>
<li class="listitem">
          Deprecated <code class="computeroutput"><span class="identifier">deadline_timer</span></code>
          and associated types.
        </li>
<li class="listitem">
          Added rvalue-qualified <code class="computeroutput"><span class="keyword">operator</span><span class="special">()</span></code> overloads to associating binders.
        </li>
<li class="listitem">
          Added support for modular build structure.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code>
          of functions that return move-only types.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">co_composed</span></code> to not
          require concepts support.
        </li>
<li class="listitem">
          Fixed the epoll reactor to not try to re-register regular file descriptors
          after fork.
        </li>
<li class="listitem">
          Fixed a leak in <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">detail</span><span class="special">::</span><span class="identifier">engine</span></code> move assignment.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h6"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_32_0___boost_1_86"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_32_0___boost_1_86">Asio
      1.32.0 / Boost 1.86</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed an issue in <code class="computeroutput"><span class="identifier">co_composed</span></code>
          caused by a missing <code class="computeroutput"><span class="identifier">decay</span></code>.
        </li>
<li class="listitem">
          Fixed an issue in <code class="computeroutput"><span class="identifier">co_composed</span></code>
          due to a missing reference in a cast to a base class type.
        </li>
<li class="listitem">
          Changed to use the standard C++20 coroutine feature test macro by default.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">aligned_alloc</span></code> on Android, when available.
        </li>
<li class="listitem">
          Fixed an integer conversion warning in <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v6</span></code>,
          on iOS/tvOS.
        </li>
<li class="listitem">
          Added missing include of <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">malloc</span><span class="special">.</span><span class="identifier">h</span><span class="special">&gt;</span></code>
          required for <code class="computeroutput"><span class="identifier">_alloca</span></code>.
        </li>
<li class="listitem">
          Changed to use a standard feature test macro to check if the standard library
          supports <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">invoke_result</span></code>.
        </li>
<li class="listitem">
          Fixed handling of <code class="computeroutput"><span class="identifier">file_base</span><span class="special">::</span><span class="identifier">append</span></code>
          in Windows file support.
        </li>
<li class="listitem">
          Fixed some warnings in IP address to string conversion.
        </li>
<li class="listitem">
          Added support for using <code class="computeroutput"><span class="identifier">co_spawn</span></code>
          when exceptions are disabled.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">spawn</span><span class="special">.</span><span class="identifier">hpp</span></code> header to be self-contained.
        </li>
<li class="listitem">
          Enabled TLS v1.3 options for WolfSSL.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code> implementation to use the correct
          cancellation slot.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">strand</span><span class="special">::</span><span class="identifier">wrap</span><span class="special">()</span></code>
          so that its return value has an associated executor.
        </li>
<li class="listitem">
          Marked <code class="computeroutput"><span class="keyword">constexpr</span></code> global variables
          as <code class="computeroutput"><span class="keyword">inline</span></code>.
        </li>
<li class="listitem">
          Documentation fixes.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h7"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_31_0"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_31_0">Asio
      1.31.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p class="simpara">
          Changed the <code class="computeroutput"><span class="identifier">default_completion_token</span></code>
          trait's primary template to select <code class="computeroutput"><span class="identifier">deferred</span></code>
          as the default completion token. As a result, most asynchronous operations'
          initiating functions will return a deferred asynchronous operation by default.
          For example, the completion token can be omitted when calling asynchronous
          operations from an <code class="computeroutput"><span class="identifier">awaitable</span></code>
          coroutine:<br>
        </p>
<pre class="programlisting"><span class="identifier">awaitable</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">echo</span><span class="special">(</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">my_socket</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">char</span> <span class="identifier">data</span><span class="special">[</span><span class="number">1024</span><span class="special">];</span>
  <span class="keyword">for</span> <span class="special">(;;)</span>
  <span class="special">{</span>
    <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">));</span>
    <span class="identifier">co_await</span> <span class="identifier">async_write</span><span class="special">(</span><span class="identifier">my_socket</span><span class="special">,</span> <span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">n</span><span class="special">));</span>
  <span class="special">}</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          or when using an operation that accepts asynchronous operations as function
          objects, such as <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">make_parallel_group</span></code>:<br>
        </p>
<pre class="programlisting"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">make_parallel_group</span><span class="special">(</span>
    <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">)),</span>
    <span class="identifier">my_timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">()</span>
  <span class="special">).</span><span class="identifier">async_wait</span><span class="special">(/*</span> <span class="special">...</span> <span class="special">*/);</span>
</pre>
</li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">is_completion_condition</span></code>
          trait and used it to add the missing default completion tokens to overloads
          of <code class="computeroutput"><span class="identifier">async_read</span></code>, <code class="computeroutput"><span class="identifier">async_read_at</span></code>, <code class="computeroutput"><span class="identifier">async_write</span></code>,
          and <code class="computeroutput"><span class="identifier">async_write_at</span></code>.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">is_connect_condition</span></code>
          trait and used it disambiguate overloads of <code class="computeroutput"><span class="identifier">async_connect</span></code>
          when the completion token is defaulted.
        </li>
<li class="listitem">
<p class="simpara">
          Extended the completion token adapters <code class="computeroutput"><span class="identifier">as_tuple</span></code>,
          <code class="computeroutput"><span class="identifier">bind_allocator</span></code>, <code class="computeroutput"><span class="identifier">bind_cancellation_slot</span></code>, <code class="computeroutput"><span class="identifier">bind_executor</span></code>, <code class="computeroutput"><span class="identifier">bind_immediate_executor</span></code>,
          and <code class="computeroutput"><span class="identifier">redirect_error</span></code> to allow
          them to be used as <span class="emphasis"><em>partial completion token adapters</em></span>.
          This means that they can be created without explicitly supplying a completion
          token. Instead, when the adapter is passed to an asynchronous operation,
          it will automatically determine the operation's default completion token
          and adapt it. For example, the expression:<br>
        </p>
<pre class="programlisting"><span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span> <span class="identifier">as_tuple</span><span class="special">)</span>
</pre>
<p class="simpara">
          will return a deferred asynchronous operation with the completion arguments
          packaged in a tuple. They may also be applied using the <code class="computeroutput"><span class="identifier">deferred</span></code>
          operations' pipe operator:<br>
        </p>
<pre class="programlisting"><span class="identifier">error_code</span> <span class="identifier">e</span><span class="special">;</span>
<span class="identifier">co_await</span> <span class="special">(</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">my_socket</span><span class="special">,</span> <span class="identifier">my_buffer</span><span class="special">)</span> <span class="special">|</span> <span class="identifier">redirect_error</span><span class="special">(</span><span class="identifier">e</span><span class="special">));</span>
</pre>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">cancel_after</span></code>
          and <code class="computeroutput"><span class="identifier">cancel_at</span></code> completion
          token adapters. These may be used to adapt any asynchronous operation to
          emit a cancellation signal after a specified duration or at an absolute
          time point. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span>
    <span class="identifier">cancel_after</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">10</span><span class="special">),</span>
      <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
      <span class="special">{</span>
        <span class="comment">// ...</span>
      <span class="special">}));</span>
</pre>
<p class="simpara">
          This cancellation is implemented internally using a <code class="computeroutput"><span class="identifier">basic_waitable_timer</span></code>.
          By default, this timer is created using the asynchronous operation's I/O
          executor. If the operation does specify its I/O executor, a timer may be
          explicitly supplied:<br>
        </p>
<pre class="programlisting"><span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span>
    <span class="identifier">cancel_after</span><span class="special">(</span><span class="identifier">my_timer</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">10</span><span class="special">),</span>
      <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
      <span class="special">{</span>
        <span class="comment">// ...</span>
      <span class="special">}));</span>
</pre>
<p class="simpara">
          These adapters may also be used as partial completion token adapters, as
          in:<br>
        </p>
<pre class="programlisting"><span class="identifier">co_await</span> <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span> <span class="identifier">cancel_after</span><span class="special">(</span><span class="number">5</span><span class="identifier">s</span><span class="special">));</span>
</pre>
<p class="simpara">
          or:<br>
        </p>
<pre class="programlisting"><span class="identifier">co_await</span> <span class="special">(</span>
    <span class="identifier">async_write</span><span class="special">(</span><span class="identifier">my_socket</span><span class="special">,</span> <span class="identifier">my_buffer</span><span class="special">)</span> <span class="special">|</span> <span class="identifier">as_tuple</span>
      <span class="special">|</span> <span class="identifier">cancel_after</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">chronos</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">10</span><span class="special">)</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          or to adapt other partial completion token adapters:<br>
        </p>
<pre class="programlisting"><span class="identifier">co_await</span> <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span> <span class="identifier">cancel_after</span><span class="special">(</span><span class="number">5</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">as_tuple</span><span class="special">));</span>
</pre>
<p class="simpara">
          Note that, since the implementation in terms of a timer introduces a parallel
          <code class="computeroutput"><span class="identifier">async_wait</span></code> operation, it
          is the responsibility of the caller to ensure that the asynchronous operation
          is performed in an implicit or explicit strand.
        </p>
</li>
<li class="listitem">
          Changed all completion token adapters to ensure they correctly propagate
          the asynchronous operation's I/O executor during adaptation.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">async_compose</span></code> and
          <code class="computeroutput"><span class="identifier">co_composed</span></code> to correctly
          indicate if they have an I/O executor.
        </li>
<li class="listitem">
          Moved <code class="computeroutput"><span class="identifier">co_composed</span></code> out of
          the <code class="computeroutput"><span class="identifier">experimental</span></code> namespace.
        </li>
<li class="listitem">
<p class="simpara">
          Added <code class="computeroutput"><span class="identifier">composed</span></code>, which creates
          an initiation function object from a stateful implementation. It is similar
          to <code class="computeroutput"><span class="identifier">co_composed</span></code>, but for
          regular function objects rather than C++20 coroutines. For example:
        </p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">async_echo_implementation</span>
<span class="special">{</span>
  <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">socket_</span><span class="special">;</span>
  <span class="identifier">mutable_buffer</span> <span class="identifier">buffer_</span><span class="special">;</span>
  <span class="keyword">enum</span> <span class="special">{</span> <span class="identifier">starting</span><span class="special">,</span> <span class="identifier">reading</span><span class="special">,</span> <span class="identifier">writing</span> <span class="special">}</span> <span class="identifier">state_</span><span class="special">;</span>

  <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Self</span><span class="special">&gt;</span>
  <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">Self</span><span class="special">&amp;</span> <span class="identifier">self</span><span class="special">,</span>
      <span class="identifier">error_code</span> <span class="identifier">error</span><span class="special">,</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="keyword">switch</span> <span class="special">(</span><span class="identifier">state_</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">}</span>
  <span class="special">}</span>
<span class="special">};</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">CompletionToken</span><span class="special">&gt;</span>
<span class="keyword">auto</span> <span class="identifier">async_echo</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">socket</span><span class="special">,</span>
    <span class="identifier">mutable_buffer</span> <span class="identifier">buffer</span><span class="special">,</span>
    <span class="identifier">CompletionToken</span><span class="special">&amp;&amp;</span> <span class="identifier">token</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">return</span> <span class="identifier">async_initiate</span><span class="special">&lt;</span><span class="identifier">CompletionToken</span><span class="special">,</span>
    <span class="keyword">void</span><span class="special">(</span><span class="identifier">error_code</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">)&gt;(</span>
      <span class="identifier">composed</span><span class="special">(</span>
        <span class="identifier">async_echo_implementation</span><span class="special">{</span><span class="identifier">socket</span><span class="special">,</span> <span class="identifier">buffer</span><span class="special">,</span>
          <span class="identifier">async_echo_implementation</span><span class="special">::</span><span class="identifier">starting</span><span class="special">},</span> <span class="identifier">socket</span><span class="special">),</span>
      <span class="identifier">token</span><span class="special">,</span> <span class="identifier">error_code</span><span class="special">{},</span> <span class="number">0</span><span class="special">);</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          The <code class="computeroutput"><span class="identifier">async_compose</span></code> function
          has been changed to be a thin wrapper around <code class="computeroutput"><span class="identifier">composed</span></code>.
          However, unlike <code class="computeroutput"><span class="identifier">async_compose</span></code>,
          <code class="computeroutput"><span class="identifier">composed</span></code> allows arguments
          to be passed to the stateful implementation when the operation is initiated.
        </p>
</li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">detached</span></code> completion
          token to work with asynchronous operations that have multiple completion
          signatures.
        </li>
<li class="listitem">
          Changed <code class="computeroutput"><span class="identifier">async_initiate</span></code>
          to allow an empty variadic list of completion signatures, which would indicate
          that an asynchronous operation never completes.
        </li>
<li class="listitem">
<p class="simpara">
          Added overloads of <code class="computeroutput"><span class="identifier">async_initiate</span></code>
          that automatically deduce the type of the completion token. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">async_initiate</span><span class="special">(</span><span class="identifier">co_composed</span><span class="special">(/*</span> <span class="special">...</span> <span class="special">*/),</span> <span class="identifier">detached</span><span class="special">,</span> <span class="identifier">arg_1</span><span class="special">,</span> <span class="identifier">arg_2</span><span class="special">);</span>
</pre>
<p class="simpara">
          will deduce the token type from the argument <code class="computeroutput"><span class="identifier">detached</span></code>.
        </p>
</li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">async_immediate</span></code> which
          implements a trivial asynchronous operation that completes immediately,
          using an associated immediate executor if available. It is intended for
          use within asynchronous compositions to make it easier to provide optimised
          immediate completion.
        </li>
<li class="listitem">
          Updated the documentation for various asynchronous operations to specify
          immediate completion in terms of <code class="computeroutput"><span class="identifier">async_immediate</span></code>.
        </li>
<li class="listitem">
          Enabled SFINAE-based partial specialisation of the <code class="computeroutput"><span class="identifier">associator</span></code>
          trait.
        </li>
<li class="listitem">
          Changed to use the recycling allocator as the fallback for all operations,
          rather than calling the underlying recycling allocation helper functions
          directly.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">deferred</span></code> implementation
          to ensure that the wrapped initiation function object's copyability is
          correctly propagated.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code> compatibility with clang 15.
        </li>
<li class="listitem">
          Fixed deduction of a completion handler's default immediate executor type.
        </li>
<li class="listitem">
          Don't use <code class="computeroutput"><span class="identifier">ioctl</span></code> to modify
          the non-blocking mode on socket or descriptors that have been assigned,
          as they may originate from an external source.
        </li>
<li class="listitem">
          Don't call <code class="computeroutput"><span class="identifier">fcntl</span></code> with
          <code class="computeroutput"><span class="identifier">F_SETFL</span></code> if the flags aren't
          changing.
        </li>
<li class="listitem">
          Don't enable non-blocking mode when performing an <code class="computeroutput"><span class="identifier">async_wait</span></code>
          operation on sockets or descriptors.
        </li>
<li class="listitem">
          Update some composed operation examples to destroy the timer object before
          calling the completion handler.
        </li>
<li class="listitem">
          Fix <code class="computeroutput"><span class="identifier">read_until</span></code> regex support
          when <code class="computeroutput"><span class="identifier">BOOST_ASIO_NO_DYNAMIC_BUFFER_V1</span></code>
          is defined.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h8"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_30_2___boost_1_85"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_30_2___boost_1_85">Asio
      1.30.2 / Boost 1.85</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">co_spawn</span></code> to correctly
          propagate exceptions resulting from cancellation to the completion handler.
        </li>
<li class="listitem">
          Added calls to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">launder</span></code> to fix undefined behaviour in
          <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>
          internal storage.
        </li>
<li class="listitem">
          Added missing handling of the <code class="computeroutput"><span class="identifier">file_base</span><span class="special">::</span><span class="identifier">append</span></code>
          flag in the Windows implementation of file support.
        </li>
<li class="listitem">
          Updated the socket and descriptor implementations to add more cases where
          they will fall back to <code class="computeroutput"><span class="identifier">fcntl</span></code>
          if a call to <code class="computeroutput"><span class="identifier">ioctl</span></code> fails.
        </li>
<li class="listitem">
          Fixed a compile error that occurred when channels and <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code>
          were both used in the same translation unit.
        </li>
<li class="listitem">
          Added missing CancellationSlot type requirements to documentation.
        </li>
<li class="listitem">
          Minor documentation updates.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h9"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_30_1"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_30_1">Asio
      1.30.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">async_result</span></code>
          primary template's concept checking to correctly handle lvalue-qualified
          completion signatures.
        </li>
<li class="listitem">
          Fixed some compile errors that could arise when using the <code class="computeroutput"><span class="identifier">bind_allocator</span></code>, <code class="computeroutput"><span class="identifier">bind_executor</span></code>,
          <code class="computeroutput"><span class="identifier">bind_immediate_executor</span></code>
          and <code class="computeroutput"><span class="identifier">bind_cancellation_slot</span></code>
          completion token adapters to adapt each other.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">ranged_parallel_group</span></code>
          operation so that it moves the <code class="computeroutput"><span class="identifier">completion_order</span></code>
          vector when invoking the completion handler.
        </li>
<li class="listitem">
          Fixed the <code class="literal">boost/asio/experimental/parallel_group.hpp</code>
          header so that it is self-contained.
        </li>
<li class="listitem">
          Fixed some warnings about deprecated implicit copy constructors on <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">basic_resolver_query</span></code>, <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">strand</span></code>,
          and <code class="computeroutput"><span class="identifier">coroutine</span></code>.
        </li>
<li class="listitem">
          Updated the version specification used to initialise Winsock.
        </li>
<li class="listitem">
          Fixed the documentation hyperlinks for the deduced return types of asynchronous
          operations' initiating functions.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h10"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_30_0___boost_1_84"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_30_0___boost_1_84">Asio
      1.30.0 / Boost 1.84</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed compatibility between <code class="computeroutput"><span class="identifier">any_completion_handler</span></code>
          and compilation using <code class="computeroutput"><span class="identifier">BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT</span></code>.
        </li>
<li class="listitem">
          Fixed a crash that may occur when attempting to access a default-constructed
          <code class="computeroutput"><span class="identifier">any_completion_handler</span></code>
          object's associators.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code>
          class's <code class="computeroutput"><span class="identifier">async_handshake</span></code>
          operation so that it works with a defaulted completion token.
        </li>
<li class="listitem">
          Updated all examples to use C++11 as the minimum language standard.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h11"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_29_0"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_29_0">Asio
      1.29.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Changed to require C++11 as the minimum language standard.
        </li>
<li class="listitem">
          Removed deprecated functionality from the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">execution</span></code>
          namespace.
        </li>
<li class="listitem">
          Removed deprecated invocation and allocation hooks.
        </li>
<li class="listitem">
          Added compatibility between Asio's placeholders and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">bind</span></code>.
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">try_send_via_dispatch</span></code>
          and <code class="computeroutput"><span class="identifier">try_send_n_via_dispatch</span></code>
          functions to channels.
        </li>
<li class="listitem">
          Improved C++11 support for multi-signature channels.
        </li>
<li class="listitem">
          Fixed compatibility between channel asynchronous operations and <code class="computeroutput"><span class="identifier">any_completion_handler</span></code>.
        </li>
<li class="listitem">
          Added missing equality operators for mixed property types belonging to
          the same category.
        </li>
<li class="listitem">
          Fixed an issue where <code class="computeroutput"><span class="identifier">spawn</span></code>-based
          stackful coroutines would terminate the program when used with asynchronous
          operations that have a completion signature starting with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span></code>.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h12"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_28_2___boost_1_83"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_28_2___boost_1_83">Asio
      1.28.2 / Boost 1.83</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed the completion token adapters <code class="computeroutput"><span class="identifier">bind_allocator</span></code>,
          <code class="computeroutput"><span class="identifier">bind_cancellation_slot</span></code>
          and <code class="computeroutput"><span class="identifier">bind_immediate_executor</span></code>
          to not require a <code class="computeroutput"><span class="identifier">return_type</span></code>
          type alias in the adapted <code class="computeroutput"><span class="identifier">async_result</span></code>
          specialisation.
        </li>
<li class="listitem">
          Fixed a potental crash due to an object lifetime issue in the <code class="computeroutput"><span class="identifier">co_spawn</span></code> operation's cancellation support.
        </li>
<li class="listitem">
          Enabled compiler-supported thread locals on more target platforms, using
          the <code class="computeroutput"><span class="keyword">thread_local</span></code> keyword if
          available.
        </li>
<li class="listitem">
          Fixed the documentation of the per-operation cancellation behaviour for
          <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">co_composed</span></code> to correctly state that terminal
          cancellation is enabled by default.
        </li>
<li class="listitem">
          Documented the per-operation cancellation behaviour of <code class="computeroutput"><span class="identifier">async_compose</span></code>.
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">bind_immediate_executor</span></code>
          to the <code class="computeroutput"><span class="identifier">Completion</span> <span class="identifier">Token</span>
          <span class="identifier">Adapters</span></code> overview.
        </li>
<li class="listitem">
          Added an example illustrating how to use an <code class="computeroutput"><span class="identifier">experimental</span>
          <span class="identifier">channel</span></code> for mutual exclusion
          between cooperating asynchronous actors.
        </li>
<li class="listitem">
          Added an example showing how to write a minimal completion executor.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h13"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_28_1"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_28_1">Asio
      1.28.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added missing compatibility with <code class="computeroutput"><span class="identifier">associated_immediate_executor</span></code>
          to <code class="computeroutput"><span class="identifier">any_completion_handler</span></code>.
        </li>
<li class="listitem">
          Fixed a null pointer dereference that occurs when using <code class="computeroutput"><span class="identifier">query</span></code>,
          <code class="computeroutput"><span class="identifier">require</span></code> or <code class="computeroutput"><span class="identifier">prefer</span></code> with an empty <code class="computeroutput"><span class="identifier">any_executor</span></code>.
        </li>
<li class="listitem">
          Added a workaround in <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code>
          for a spurious syntax error when compiling with MSVC.
        </li>
<li class="listitem">
          Fixed an integer truncation issue in per-operation cancellation, when using
          the reactor backend on 64-bit Windows.
        </li>
<li class="listitem">
          Added a compile-time check for a minimum Linux kernel version of 5.10,
          when <code class="literal">io_uring</code> support is enabled.
        </li>
<li class="listitem">
          Fixed a compile error in the converting move constructors for <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">basic_channel</span></code> and <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">basic_concurrent_channel</span></code>.
        </li>
<li class="listitem">
          Fixed a memory leak on some <code class="computeroutput"><span class="identifier">signal_set</span></code>
          error handling code paths.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">bad_address_cast</span></code>
          to not use a deprecated implicit copy constructor.
        </li>
<li class="listitem">
          Fixed a copy/paste error in the <code class="computeroutput"><span class="identifier">dev_poll_reactor</span></code>
          backend.
        </li>
<li class="listitem">
          Fixed the <code class="literal">io_uring</code> backend to ensure the internal timeout
          operations, used to implement <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">run_for</span></code>
          and <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">run_until</span></code>, are cleaned up correctly.
        </li>
<li class="listitem">
          Eliminated some duplicated state in the <code class="computeroutput"><span class="identifier">co_spawn</span></code>
          implementation's entry point, reducing memory consumption.
        </li>
<li class="listitem">
          Added missing c++14 echo examples.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h14"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_28_0___boost_1_82"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_28_0___boost_1_82">Asio
      1.28.0 / Boost 1.82</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added missing handler tracking source location support to <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>-based
          coroutine's ability to <code class="computeroutput"><span class="identifier">co_await</span></code>
          asynchronous operations packaged as function objects.
        </li>
<li class="listitem">
          Add missing handler tracking source location support to <code class="computeroutput"><span class="identifier">co_composed</span></code>.
        </li>
<li class="listitem">
          Fixed suppression of spurious 'potential null dereference' warnings, to
          work with older compilers.
        </li>
<li class="listitem">
          Fixed a bug where passing the deprecated <code class="computeroutput"><span class="identifier">const_buffers_1</span></code>
          and <code class="computeroutput"><span class="identifier">mutable_buffers_1</span></code> types
          to <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">()</span></code>
          would result in the contiguous iterator overloads being incorrectly chosen.
        </li>
<li class="listitem">
          Disabled the runtime Windows version test unless targeting older Windows
          versions.
        </li>
<li class="listitem">
          Fixed compatibility between buffered stream wrappers and move-constructible
          streams, such as <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code>.
        </li>
<li class="listitem">
          Marked <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v4</span><span class="special">::</span><span class="identifier">to_ulong</span></code> as deprecated in the documentation.
        </li>
<li class="listitem">
          Fixed shadowed variable warnings.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">basic_socket_acceptor</span><span class="special">::</span><span class="identifier">async_accept</span></code>
          concept requirement checking to be compatible with lambdas that have a
          deduced return type.
        </li>
<li class="listitem">
          Fixed a feature detection macro used in <code class="computeroutput"><span class="identifier">use_future</span></code>'s
          compatibility traits.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">as_tuple</span></code> compatibility
          with legacy completion tokens.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">redirect_error</span></code> compatibility
          with new completion tokens.
        </li>
<li class="listitem">
          Fixed a potential, Windows-specific program termination due to exceptions
          that should have been allowed to escape from a destructor.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">this_coro</span></code> to prevent
          inadvertent <code class="computeroutput"><span class="identifier">co_await</span></code> of
          boolean expressions.
        </li>
<li class="listitem">
          Fixed result handling in <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">use_coro</span></code>
          implementation.
        </li>
<li class="listitem">
          Fixed variadic template emulation for <code class="computeroutput"><span class="identifier">is_async_operation</span></code>
          and <code class="computeroutput"><span class="identifier">completion_signature_of</span></code>.
        </li>
<li class="listitem">
          Fixed incorrect reuse of a moved-from result in <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span></code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code> use with custom allocators.
        </li>
<li class="listitem">
          Fixed clean up of internal I/O object structures when using <code class="literal">io_uring</code>.
        </li>
<li class="listitem">
          Use cached offset when seeking a file with seek_cur on Windows.
        </li>
<li class="listitem">
          Added immediate completion to asynchronous operation requirements.
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">any_completion_handler</span><span class="special">&lt;&gt;</span></code>, <code class="computeroutput"><span class="identifier">co_composed</span></code>,
          and immediate completion support to the documentation overview.
        </li>
<li class="listitem">
          Added buffer literals to the documentation.
        </li>
<li class="listitem">
          Added a link to the <a href="https://github.com/chriskohlhoff/asio-debugger-extensions" target="_top">Asio
          debugger extensions</a> repository.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h15"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_27_0"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_27_0">Asio
      1.27.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p class="simpara">
          Added the ability to customise the execution of a completion handler when
          an operation completes immediately. This change adds the <code class="computeroutput"><span class="identifier">associated_immediate_executor</span></code> associator
          trait, <code class="computeroutput"><span class="identifier">bind_immediate_executor</span></code>
          function, and <code class="computeroutput"><span class="identifier">immediate_executor_binder</span></code>
          adapter. When a supported operation completes immediately (that is, within
          the initiating function) the associated immmediate executor is obtained,
          and the completion handler is delivered through that executor as if by
          using <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">dispatch</span></code> on that executor. By default,
          the immediate executor delivers the completion handler as if using <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">post</span></code> via the operation's I/O executor.
          For example, to allow a recursive call to the completion handler of an
          <code class="computeroutput"><span class="identifier">async_read_some</span></code> operation,
          we may specify that immediate completion is delivered via a <code class="computeroutput"><span class="identifier">system_executor</span></code>:<br>
        </p>
<pre class="programlisting"><span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span>
    <span class="identifier">bind_immediate_executor</span><span class="special">(</span>
      <span class="identifier">system_executor</span><span class="special">(),</span>
      <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
      <span class="special">{</span>
        <span class="comment">// ...</span>
      <span class="special">}</span>
    <span class="special">)</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br> Immediate execution is currently supported for asynchronous operations
          on reactor-based sockets and descriptors, and for asynchronous operations
          on channels.
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added user-defined literals for buffer types. The <code class="computeroutput"><span class="identifier">_buf</span></code>
          literal suffix, defined in namespace <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer_literals</span></code>,
          may be used to create const_buffer objects from string, binary integer,
          and hexadecimal integer literals. These buffer literals may be arbitrarily
          long. For example:<br>
        </p>
<pre class="programlisting">  using namespace asio::buffer_literals;

  asio::const_buffer b1 = "hello"_buf;
  asio::const_buffer b2 = 0xdeadbeef_buf;
  asio::const_buffer b3 = 0x0123456789abcdef0123456789abcdef_buf;
  asio::const_buffer b4 = 0b1010101011001100_buf;
  </pre>
<p class="simpara">
          <br> The memory associated with a buffer literal is valid for the lifetime
          of the program. This means that the buffer can be safely used with asynchronous
          operations:<br>
        </p>
<pre class="programlisting"><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">my_socket</span><span class="special">,</span> <span class="string">"hello"</span><span class="identifier">_buf</span><span class="special">,</span> <span class="identifier">my_handler</span><span class="special">);</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Added a new protocol type <code class="computeroutput"><span class="identifier">local</span><span class="special">::</span><span class="identifier">seq_packet_protocol</span></code>
          to represent <code class="computeroutput"><span class="identifier">AF_UNIX</span></code> with
          <code class="computeroutput"><span class="identifier">SOCK_SEQPACKET</span></code>.
        </li>
<li class="listitem">
<p class="simpara">
          Exposed <code class="computeroutput"><span class="identifier">sigaction</span><span class="special">()</span></code>
          flags via optional argument to <code class="computeroutput"><span class="identifier">signal_set</span><span class="special">::</span><span class="identifier">add</span></code>.
          When registering a signal, it is now possible to pass flags that specify
          the behaviour associated with the signal. These flags are specified as
          an enum type in a new class, signal_set_base, and are passed to the underlying
          <code class="computeroutput"><span class="identifier">sigaction</span><span class="special">()</span></code>
          call. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">signal_set</span> <span class="identifier">sigs</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>
<span class="identifier">sigs</span><span class="special">.</span><span class="identifier">add</span><span class="special">(</span><span class="identifier">SIGINT</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">signal_set</span><span class="special">::</span><span class="identifier">flags</span><span class="special">::</span><span class="identifier">restart</span><span class="special">);</span>
</pre>
<p class="simpara">
          <br> Specifying flags other than <code class="computeroutput"><span class="identifier">flags</span><span class="special">::</span><span class="identifier">dont_care</span></code>
          will fail unless <code class="computeroutput"><span class="identifier">sigaction</span><span class="special">()</span></code> is supported by the target operating
          system. Since signal registration is global, conflicting flags (multiple
          registrations that pass differing flags other than <code class="computeroutput"><span class="identifier">flags</span><span class="special">::</span><span class="identifier">dont_care</span></code>)
          will also result in an error.
        </p>
</li>
<li class="listitem">
          Change <code class="computeroutput"><span class="identifier">allocator_binder</span></code>,
          <code class="computeroutput"><span class="identifier">executor_binder</span></code>, and <code class="computeroutput"><span class="identifier">cancellation_slot_binder</span></code> to support detection
          of unspecialised associators.
        </li>
<li class="listitem">
          Fixed ambiguity in <code class="computeroutput"><span class="identifier">associated_cancellation_slot</span><span class="special">&lt;</span><span class="identifier">reference_wrapper</span><span class="special">&gt;::</span><span class="identifier">get</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">awaitable</span></code> handling
          for completion signatures containing <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span></code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">channel</span></code> <code class="computeroutput"><span class="identifier">try_send</span></code>
          failure after a <code class="computeroutput"><span class="identifier">cancel</span></code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">thread_pool</span><span class="special">::</span><span class="identifier">join</span><span class="special">()</span></code>
          deadlock when the pool has no internal threads.
        </li>
<li class="listitem">
          Fixed pipe <code class="computeroutput"><span class="identifier">release</span><span class="special">()</span></code>
          when using <code class="literal">io_uring</code>.
        </li>
<li class="listitem">
          Fixed a data initialisation issue in the <code class="literal">io_uring</code> backend.
        </li>
<li class="listitem">
          Fixed a dangling reference issue in the execution context overload of
          <code class="computeroutput"><span class="identifier">get_associated_executor</span></code>.
        </li>
<li class="listitem">
          Ensured buffered messages can still be received when an <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">channel</span></code>
          is closed.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">any_completion_handler</span></code>
          assignment operator to work correctly.
        </li>
<li class="listitem">
          Constrained the constructor of the move-only class template <code class="computeroutput"><span class="identifier">any_completion_handler</span></code> to prevent accidental
          copying
        </li>
<li class="listitem">
          Suppressed spurious 'potential null dereference' warnings.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="identifier">uint64_t</span></code>
          for OpenSSL options, to match OpenSSL 3.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">deferred</span></code> interoperability
          with multiple completion signatures.
        </li>
<li class="listitem">
          Fixed channels to support C++14, and to partially support C++11. C++11
          support is limited to channels with a single completion signature, or channels
          with a void() signature (plus the error signature added by the channel
          traits).
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">any_completion_handler</span></code>
          to the documentation.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h16"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_26_0___boost_1_81"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_26_0___boost_1_81">Asio
      1.26.0 / Boost 1.81</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">spawn</span></code> and <code class="computeroutput"><span class="identifier">co_spawn</span></code> implementations to dispatch
          cancellation handlers on the correct executor. When a completion handler
          uses a specified (i.e. non-default) associated executor, cancellation handlers
          are dispatched to the executor that was passed to <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">co_spawn</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">spawn</span></code> to ensure the
          completion handler is dispatched through the correct executor.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="identifier">snprintf</span></code>
          rather than <code class="computeroutput"><span class="identifier">sprintf</span></code> on
          latest Xcode, to address deprecation warnings.
        </li>
<li class="listitem">
          Fixed compatibility between <code class="computeroutput"><span class="identifier">co_spawn</span></code>
          and <code class="computeroutput"><span class="identifier">any_completion_handler</span></code>.
        </li>
<li class="listitem">
          Fixed the arguments passed to <code class="computeroutput"><span class="identifier">select_reactor</span><span class="special">::</span><span class="identifier">run</span></code>
          when it is run on an internal thread.
        </li>
<li class="listitem">
          Fixed compilation errors when <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_SMALL_BLOCK_RECYCLING</span></code>
          is defined.
        </li>
<li class="listitem">
          Updated detection of C++20 coroutine support on clang 14 and later. This
          includes the ability to use coroutines with libstdc++.
        </li>
<li class="listitem">
          Changed standard library feature detection to always enable <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">invoke_result</span></code> when targeting C++17 or
          later.
        </li>
<li class="listitem">
          Fixed detection of return type deduction with MSVC.
        </li>
<li class="listitem">
          Added a missing include in <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code>
          implementation.
        </li>
<li class="listitem">
          Updated the asynchronous operation requirements to relax the requirements
          on the associated executor.
        </li>
<li class="listitem">
          Added <code class="literal">io_uring</code> to the implementation notes.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h17"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_25_0"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_25_0">Asio
      1.25.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">consign</span></code> completion
          token adapter, which can be used to attach additional values to a completion
          handler. This is typically used to keep at least one copy of an object,
          such as a smart pointer, alive until the completion handler is called.
          For example:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">timer1</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_shared</span><span class="special">&lt;</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span><span class="special">&gt;(</span><span class="identifier">my_io_context</span><span class="special">);</span>
<span class="identifier">timer1</span><span class="special">-&gt;</span><span class="identifier">expires_after</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
<span class="identifier">timer1</span><span class="special">-&gt;</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">consign</span><span class="special">(</span>
      <span class="special">[](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">)</span>
      <span class="special">{</span>
        <span class="comment">// ...</span>
      <span class="special">},</span>
      <span class="identifier">timer1</span>
    <span class="special">)</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added <code class="computeroutput"><span class="identifier">any_completion_handler</span><span class="special">&lt;&gt;</span></code>, which can be used to type-erase
          completion handlers. A typical use case is to enable separate compilation
          of asynchronous operation implementations. For example:<br>
        </p>
<pre class="programlisting"><span class="comment">// Header file:</span>

<span class="keyword">void</span> <span class="identifier">async_sleep_impl</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">any_completion_handler</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">)&gt;</span> <span class="identifier">handler</span><span class="special">,</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">any_io_executor</span> <span class="identifier">ex</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">nanoseconds</span> <span class="identifier">duration</span><span class="special">);</span>

<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">CompletionToken</span><span class="special">&gt;</span>
<span class="keyword">inline</span> <span class="keyword">auto</span> <span class="identifier">async_sleep</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">any_io_executor</span> <span class="identifier">ex</span><span class="special">,</span>
    <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">nanoseconds</span> <span class="identifier">duration</span><span class="special">,</span> <span class="identifier">CompletionToken</span><span class="special">&amp;&amp;</span> <span class="identifier">token</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">return</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_initiate</span><span class="special">&lt;</span>
    <span class="identifier">CompletionToken</span><span class="special">,</span> <span class="keyword">void</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">)&gt;(</span>
      <span class="identifier">async_sleep_impl</span><span class="special">,</span> <span class="identifier">token</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">ex</span><span class="special">),</span> <span class="identifier">duration</span><span class="special">);</span>
<span class="special">}</span>

<span class="comment">// Separately compiled source file:</span>

<span class="keyword">void</span> <span class="identifier">async_sleep_impl</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">any_completion_handler</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">)&gt;</span> <span class="identifier">handler</span><span class="special">,</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">any_io_executor</span> <span class="identifier">ex</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">nanoseconds</span> <span class="identifier">duration</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">auto</span> <span class="identifier">timer</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_shared</span><span class="special">&lt;</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span><span class="special">&gt;(</span><span class="identifier">ex</span><span class="special">,</span> <span class="identifier">duration</span><span class="special">);</span>
  <span class="identifier">timer</span><span class="special">-&gt;</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">consign</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">handler</span><span class="special">),</span> <span class="identifier">timer</span><span class="special">));</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">co_composed</span></code> which facilitates a lightweight
          implementation of user-defined asynchronous operations using C++20 coroutines.
          The following example illustrates a simple asynchronous operation that
          implements an echo protocol in terms of a coroutine:<br>
        </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">CompletionToken</span><span class="special">&gt;</span>
<span class="keyword">auto</span> <span class="identifier">async_echo</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">socket</span><span class="special">,</span>
    <span class="identifier">CompletionToken</span><span class="special">&amp;&amp;</span> <span class="identifier">token</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">return</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_initiate</span><span class="special">&lt;</span>
    <span class="identifier">CompletionToken</span><span class="special">,</span> <span class="keyword">void</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">)&gt;(</span>
      <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">co_composed</span><span class="special">&lt;</span>
        <span class="keyword">void</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">)&gt;(</span>
          <span class="special">[](</span><span class="keyword">auto</span> <span class="identifier">state</span><span class="special">,</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">socket</span><span class="special">)</span> <span class="special">-&gt;</span> <span class="keyword">void</span>
          <span class="special">{</span>
            <span class="keyword">try</span>
            <span class="special">{</span>
              <span class="identifier">state</span><span class="special">.</span><span class="identifier">throw_if_cancelled</span><span class="special">(</span><span class="keyword">true</span><span class="special">);</span>
              <span class="identifier">state</span><span class="special">.</span><span class="identifier">reset_cancellation_state</span><span class="special">(</span>
                <span class="identifier">asio</span><span class="special">::</span><span class="identifier">enable_terminal_cancellation</span><span class="special">());</span>

              <span class="keyword">for</span> <span class="special">(;;)</span>
              <span class="special">{</span>
                <span class="keyword">char</span> <span class="identifier">data</span><span class="special">[</span><span class="number">1024</span><span class="special">];</span>
                <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span>
                    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">),</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">);</span>

                <span class="identifier">co_await</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket</span><span class="special">,</span>
                    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">n</span><span class="special">),</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">);</span>
              <span class="special">}</span>
            <span class="special">}</span>
            <span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">system_error</span><span class="special">&amp;</span> <span class="identifier">e</span><span class="special">)</span>
            <span class="special">{</span>
              <span class="identifier">co_return</span> <span class="special">{</span><span class="identifier">e</span><span class="special">.</span><span class="identifier">code</span><span class="special">()};</span>
            <span class="special">}</span>
          <span class="special">},</span> <span class="identifier">socket</span><span class="special">),</span>
      <span class="identifier">token</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">socket</span><span class="special">));</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Add range-based experimental::make_parallel_group() overloads that may
          be used to launch a dynamically-sized set of asynchronous operations, where
          all operations are the same type. For example:<br>
        </p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">op_type</span> <span class="special">=</span> <span class="keyword">decltype</span><span class="special">(</span>
    <span class="identifier">socket1</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span>
      <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data1</span><span class="special">),</span>
      <span class="identifier">asio</span><span class="special">::</span><span class="identifier">deferred</span>
    <span class="special">)</span>
  <span class="special">);</span>

<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">op_type</span><span class="special">&gt;</span> <span class="identifier">ops</span><span class="special">;</span>
<span class="identifier">ops</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span>
    <span class="identifier">socket1</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span>
      <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data1</span><span class="special">),</span>
      <span class="identifier">asio</span><span class="special">::</span><span class="identifier">deferred</span>
    <span class="special">)</span>
  <span class="special">);</span>
<span class="identifier">ops</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span>
    <span class="identifier">socket2</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span>
      <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data2</span><span class="special">),</span>
      <span class="identifier">asio</span><span class="special">::</span><span class="identifier">deferred</span>
    <span class="special">)</span>
  <span class="special">);</span>

<span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">make_parallel_group</span><span class="special">(</span><span class="identifier">ops</span><span class="special">).</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">wait_for_all</span><span class="special">(),</span>
    <span class="special">[](</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">completion_order</span><span class="special">,</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&gt;</span> <span class="identifier">e</span><span class="special">,</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">n</span>
      <span class="special">)</span>
    <span class="special">{</span>
      <span class="keyword">for</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special">&lt;</span> <span class="identifier">completion_order</span><span class="special">.</span><span class="identifier">size</span><span class="special">();</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span>
      <span class="special">{</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">idx</span> <span class="special">=</span> <span class="identifier">completion_order</span><span class="special">[</span><span class="identifier">i</span><span class="special">];</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"socket "</span> <span class="special">&lt;&lt;</span> <span class="identifier">idx</span> <span class="special">&lt;&lt;</span> <span class="string">" finished: "</span><span class="special">;</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">e</span><span class="special">[</span><span class="identifier">idx</span><span class="special">]</span> <span class="special">&lt;&lt;</span> <span class="string">", "</span> <span class="special">&lt;&lt;</span> <span class="identifier">n</span><span class="special">[</span><span class="identifier">idx</span><span class="special">]</span> <span class="special">&lt;&lt;</span> <span class="string">"\n"</span><span class="special">;</span>
      <span class="special">}</span>
    <span class="special">}</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br> Thanks go to Klemens Morgenstern for supplying part of this implementation.
        </p>
</li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">any_completion_executor</span></code>,
          a type-erased wrappers for executors that are associated with completion
          handlers.
        </li>
<li class="listitem">
          Added missing <code class="computeroutput"><span class="identifier">context</span></code> query
          to use_future's executor.
        </li>
<li class="listitem">
          Added nothrow constructor overloads to <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">any_executor</span><span class="special">&lt;&gt;</span></code> and <code class="computeroutput"><span class="identifier">any_io_executor</span></code>.
        </li>
<li class="listitem">
          Optimised representation of empty <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">any_executor</span></code>
          objects to improve the performance of copy and move operations.
        </li>
<li class="listitem">
          Added an <code class="computeroutput"><span class="identifier">associated_cancellation_slot</span></code>
          specialisation for <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">reference_wrapper</span></code>.
        </li>
<li class="listitem">
          Changed I/O objects to return their executors by const reference.
        </li>
<li class="listitem">
          Changed associated to use deduced return types for all two-argument <code class="computeroutput"><span class="identifier">get</span></code> functions.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">spawn</span></code> implementation
          to catch unhandled exceptions and rethrow them outside of the spawned "thread".
        </li>
<li class="listitem">
          Fixed cleanup of of terminal-state <code class="computeroutput"><span class="identifier">spawn</span></code>
          "thread" objects.
        </li>
<li class="listitem">
          Changed semantics of 'dispatch' to mean the executor is used as-is. An
          execution context's default executor is imbued with the possibly-blocking
          property.
        </li>
<li class="listitem">
          Deprecated the <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">execute</span></code>
          customisation point. Use <code class="computeroutput"><span class="identifier">execute</span></code>
          as a member function.
        </li>
<li class="listitem">
          Deprecated the concepts, traits, functions and customisation points related
          to senders and receivers.
        </li>
<li class="listitem">
          Added a C++11 <code class="computeroutput"><span class="identifier">parallel_group</span></code>
          example.
        </li>
<li class="listitem">
          Fixed example code to not use the deprecated conversion of a resolve result
          to an endpoint.
        </li>
<li class="listitem">
          Fixed an ambiguity in <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">channel_traits</span></code>
          specialisations.
        </li>
<li class="listitem">
          Added a specialised channel implementation for the for <code class="computeroutput"><span class="identifier">R</span><span class="special">(</span><span class="identifier">error_code</span><span class="special">)</span></code> signature.
        </li>
<li class="listitem">
          Made <code class="computeroutput"><span class="identifier">cancelled</span><span class="special">()</span></code>
          public on the <code class="computeroutput"><span class="identifier">async_compose</span></code>
          'self' object.
        </li>
<li class="listitem">
          Added io_executor_type and get_io_executor to the <code class="computeroutput"><span class="identifier">async_compose</span></code>
          'self' object.
        </li>
<li class="listitem">
          Fixed implementation of <code class="computeroutput"><span class="identifier">release</span><span class="special">()</span></code> for Windows overlapped handles.
        </li>
<li class="listitem">
          Enabled deferred awaiting for <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code>,
          regularised <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">use_coro</span></code>,
          and fixed allocator handling. This means that <code class="computeroutput"><span class="identifier">use_coro</span></code>
          does not return a coro object, just like use_awaitable does, i.e. it's
          an overhead that buys us type erasure. Allocators can now be set for <code class="computeroutput"><span class="identifier">coro</span></code> by including <code class="computeroutput"><span class="identifier">allocator_arg</span></code>
          in the coro signature.
        </li>
<li class="listitem">
          Cleaned up <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span></code>
          and made it an asynchronous operation object.
        </li>
<li class="listitem">
          Constrained <code class="computeroutput"><span class="identifier">post</span></code>/<code class="computeroutput"><span class="identifier">defer</span></code> overloads on ability to require
          <code class="computeroutput"><span class="identifier">blocking</span><span class="special">.</span><span class="identifier">never</span></code>.
        </li>
<li class="listitem">
          Changed descriptor implementation to fall back to <code class="computeroutput"><span class="identifier">fcntl</span></code>
          if <code class="computeroutput"><span class="identifier">ioctl</span></code> fails with <code class="computeroutput"><span class="identifier">ENOTTY</span></code> when setting non-blocking mode.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h18"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_24_0___boost_1_80"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_24_0___boost_1_80">Asio
      1.24.0 / Boost 1.80</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added a deduced trailing return type, using <code class="computeroutput"><span class="keyword">decltype</span></code>,
          to all asynchronous operations' initiating functions when using C++11.
          This change enables the new form of <code class="computeroutput"><span class="identifier">async_result</span></code>,
          where the return type can vary per operation, for C++11.
        </li>
<li class="listitem">
          Moved <code class="computeroutput"><span class="identifier">append</span></code>, <code class="computeroutput"><span class="identifier">prepend</span></code>, <code class="computeroutput"><span class="identifier">as_tuple</span></code>,
          and <code class="computeroutput"><span class="identifier">deferred</span></code> to the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span></code> namespace, and made them compatible
          with C++11. These are no longer experimental facilities, although the names
          have temporarily been retained under the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span></code>
          namespace for backwards compatibility.
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">buffer</span><span class="special">()</span></code>
          overloads for contiguous containers, such as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">span</span></code>.
        </li>
<li class="listitem">
<p class="simpara">
          Added the ability for <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>-based coroutines to directly <code class="computeroutput"><span class="identifier">co_await</span></code> operations that are packaged
          as function objects. For example, using <code class="computeroutput"><span class="identifier">deferred</span></code>:<br>
        </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">awaitable</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">my_coro</span><span class="special">()</span>
<span class="special">{</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">timer</span><span class="special">(</span><span class="identifier">co_await</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">this_coro</span><span class="special">::</span><span class="identifier">executor</span><span class="special">);</span>
  <span class="identifier">timer</span><span class="special">.</span><span class="identifier">expires_after</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">5</span><span class="special">));</span>

  <span class="identifier">co_await</span> <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">);</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          or with a handcrafted function object:<br>
        </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">awaitable</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">my_coro</span><span class="special">()</span>
<span class="special">{</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">timer</span><span class="special">(</span><span class="identifier">co_await</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">this_coro</span><span class="special">::</span><span class="identifier">executor</span><span class="special">);</span>
  <span class="identifier">timer</span><span class="special">.</span><span class="identifier">expires_after</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">5</span><span class="special">));</span>

  <span class="identifier">co_await</span> <span class="special">[&amp;](</span><span class="keyword">auto</span><span class="special">&amp;&amp;</span> <span class="identifier">token</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="keyword">return</span> <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">token</span><span class="special">)&gt;(</span><span class="identifier">token</span><span class="special">));</span>
  <span class="special">};</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Changed <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code>
          to be a completion token-based asynchronous operation. This introduces
          new <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code>
          overloads that conform to the requirements for asynchronous operations.
          For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">do_read</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">yield_context</span> <span class="identifier">yield</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">char</span> <span class="identifier">data</span><span class="special">[</span><span class="number">1024</span><span class="special">];</span>
  <span class="identifier">size_t</span> <span class="identifier">n</span> <span class="special">=</span> <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">),</span> <span class="identifier">yield</span><span class="special">);</span>
  <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">n</span><span class="special">);</span>
<span class="special">}</span>

<span class="identifier">asio</span><span class="special">::</span><span class="identifier">spawn</span><span class="special">(</span><span class="identifier">my_executor</span><span class="special">,</span> <span class="identifier">do_read</span><span class="special">,</span>
    <span class="special">[](</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span> <span class="identifier">ex</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">result</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">});</span>
</pre>
<p class="simpara">
          These new <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code>
          overloads support cancellation, and the <code class="computeroutput"><span class="identifier">basic_yield_context</span></code>
          completion token has also been enhanced to support move-only and variadic
          result types. When targeting C++11 and later, these functions are implemented
          in terms of Boost.Context directly. The existing overloads have been retained
          but are deprecated.
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">is_async_operation</span></code>
          trait and <code class="computeroutput"><span class="identifier">async_operation</span></code>
          concept. The <code class="computeroutput"><span class="identifier">is_async_operation</span></code>
          trait may be used to determine if a function object, and optional arguments,
          may be called to initiate an asynchronous operation. For example, when
          using <code class="computeroutput"><span class="identifier">deferred</span></code>:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">d</span> <span class="special">=</span> <span class="identifier">my_timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">);</span>
<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">is_async_operation</span><span class="special">&lt;</span><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">d</span><span class="special">)&gt;::</span><span class="identifier">value</span><span class="special">);</span>
</pre>
<p class="simpara">
          <br> or with a handcrafted asynchronous operation:<br>
        </p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_async_op</span>
<span class="special">{</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">socket_</span> <span class="special">=</span> <span class="special">...;</span>

  <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Token</span><span class="special">&gt;</span>
  <span class="keyword">auto</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">const_buffer</span> <span class="identifier">data</span><span class="special">,</span> <span class="identifier">Token</span><span class="special">&amp;&amp;</span> <span class="identifier">token</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="keyword">return</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket_</span><span class="special">,</span> <span class="identifier">data</span><span class="special">,</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span><span class="identifier">Token</span><span class="special">&gt;(</span><span class="identifier">token</span><span class="special">));</span>
  <span class="special">}</span>
<span class="special">};</span>

<span class="keyword">static_assert</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">is_async_operation</span><span class="special">&lt;</span>
      <span class="identifier">my_async_op</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">const_buffer</span><span class="special">&gt;::</span><span class="identifier">value</span><span class="special">);</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">completion_signature_of</span></code>
          trait. The <code class="computeroutput"><span class="identifier">completion_signature_of</span></code>
          trait (and corresponding type alias <code class="computeroutput"><span class="identifier">completion_signature_of_t</span></code>)
          may be used to determine the completion signature of an asynchronous operation.
          For example:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">d</span> <span class="special">=</span> <span class="identifier">my_timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">);</span>
<span class="keyword">using</span> <span class="identifier">sig</span> <span class="special">=</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">completion_signature_of</span><span class="special">&lt;</span><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">d</span><span class="special">)&gt;::</span><span class="identifier">type</span><span class="special">;</span>
<span class="comment">// sig is void(error_code)</span>
</pre>
<p class="simpara">
          <br> or with a handcrafted asynchronous operation:<br>
        </p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_async_op</span>
<span class="special">{</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">socket_</span> <span class="special">=</span> <span class="special">...;</span>

  <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Token</span><span class="special">&gt;</span>
  <span class="keyword">auto</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">const_buffer</span> <span class="identifier">data</span><span class="special">,</span> <span class="identifier">Token</span><span class="special">&amp;&amp;</span> <span class="identifier">token</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="keyword">return</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket_</span><span class="special">,</span> <span class="identifier">data</span><span class="special">,</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span><span class="identifier">Token</span><span class="special">&gt;(</span><span class="identifier">token</span><span class="special">));</span>
  <span class="special">}</span>
<span class="special">};</span>

<span class="keyword">using</span> <span class="identifier">sig</span> <span class="special">=</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">completion_signature_of</span><span class="special">&lt;</span>
    <span class="identifier">my_async_op</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">const_buffer</span><span class="special">&gt;::</span><span class="identifier">type</span><span class="special">;</span>
<span class="comment">// sig is void(error_code, size_t)</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Added converting move construction/assignment to posix descriptors, serial
          ports, pipes, Windows <code class="computeroutput"><span class="identifier">object_handle</span></code>,
          Windows stream handles, and Windows random-access handles.
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">release</span><span class="special">()</span></code>
          member functions to pipes, Windows stream handles, and Windows random-access
          handles.
        </li>
<li class="listitem">
          Enabled support for <code class="computeroutput"><span class="identifier">Endpoint</span></code>
          implementations that return <code class="computeroutput"><span class="keyword">void</span></code>
          pointers from their <code class="computeroutput"><span class="identifier">data</span><span class="special">()</span></code> member functions, as per the documented
          <code class="computeroutput"><span class="identifier">Endpoint</span></code> type requirements.
        </li>
<li class="listitem">
          Removed <code class="computeroutput"><span class="identifier">all</span><span class="special">()</span></code>
          and <code class="computeroutput"><span class="identifier">race</span><span class="special">()</span></code>
          from <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span></code>, as <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">parallel_group</span></code>
          covers this functionality.
        </li>
<li class="listitem">
          Added source locations to exceptions and error codes produced by the synchronous
          and asynchronous operations.
        </li>
<li class="listitem">
          Fixed compatibility with OpenSSL 3.0.4 and later.
        </li>
<li class="listitem">
          Fixed compatibility with with <code class="literal">-masm=intel</code>.
        </li>
<li class="listitem">
          Explicitly stated that socket <code class="computeroutput"><span class="identifier">shutdown</span><span class="special">()</span></code> calls are thread-safe with respect to
          certain other synchronous operations on the same socket.
        </li>
<li class="listitem">
          Optimised the move construction of I/O objects where only the executor
          type differs.
        </li>
<li class="listitem">
          Fixed the detection of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">invoke_result</span></code>
          for clang/libc++.
        </li>
<li class="listitem">
          Fixed an issue where <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">parallel_group</span></code>
          initiation incorrectly moved arguments instead of forwarding them.
        </li>
<li class="listitem">
          Fixed a sequencing issue in the implementation of <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">dispatch</span><span class="special">()</span></code>, and <code class="computeroutput"><span class="identifier">defer</span><span class="special">()</span></code>, where the the associated allocator may
          be obtained from an already moved-from completion handler.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>
          implementation to propagate exceptions from awaited initiation functions
          through the current completion handler.
        </li>
<li class="listitem">
          Fixed detection of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">aligned_alloc</span></code>
          with <code class="literal">gcc</code> 7.
        </li>
<li class="listitem">
          Changed to avoid using the soon-to-be-deprecated <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">aligned_storage</span></code>
          on newer compilers.
        </li>
<li class="listitem">
          Fixed detection of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">aligned_alloc</span></code>
          for older Apple platforms.
        </li>
<li class="listitem">
          Removed faulty assertions from <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code>
          implementation.
        </li>
<li class="listitem">
          Added defence against Qt-defined macros when building with Intel C++.
        </li>
<li class="listitem">
          Changed the implementation of the <code class="computeroutput"><span class="identifier">select_reactor</span></code>,
          on Windows, to ensure that any exception resulting from failure to recreate
          its interrupter's sockets will be allowed to propagate out through <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">run</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Fixed various compiler warnings.
        </li>
<li class="listitem">
          Updated all composed operations examples, and the C++11 timeouts example,
          to use the new <code class="computeroutput"><span class="identifier">async_result</span></code>
          form.
        </li>
<li class="listitem">
          Added composed operation and coroutine examples for C++20.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h19"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_22_2___boost_1_79"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_22_2___boost_1_79">Asio
      1.22.2 / Boost 1.79</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          On Windows, changed the file support to open files using the same sharing
          mode as <code class="computeroutput"><span class="identifier">fopen</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          On Linux, fixed the UNIX domain sockets implementation to correctly handle
          <code class="computeroutput"><span class="identifier">EAGAIN</span></code> as an indication
          of an in-progress connect operation.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">basic_channel</span><span class="special">::</span><span class="identifier">reset</span><span class="special">()</span></code>
          and <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">basic_concurrent_channel</span><span class="special">::</span><span class="identifier">reset</span><span class="special">()</span></code>
          so that they work correctly for an unclosed channel.
        </li>
<li class="listitem">
          Fixed potential undefined behaviour in the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span></code>
          operations <code class="computeroutput"><span class="identifier">race</span><span class="special">()</span></code>
          and <code class="computeroutput"><span class="identifier">all</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">co_spawn</span></code> implementation
          to explicitly dispatch cancellation signals through the specified executor,
          if the the completion handler has an associated executor of its own.
        </li>
<li class="listitem">
          Added more detailed reference documentation to <code class="computeroutput"><span class="identifier">make_strand</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">make_work_guard</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v4</span></code>,
          <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v6</span></code>, <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">basic_channel</span></code>,
          and <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">basic_concurrent_channel</span></code>.
        </li>
<li class="listitem">
          Re-arranged and extended the Overview documentation to cover files, pipes,
          <code class="computeroutput"><span class="identifier">async_compose</span></code>, <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">deferred</span></code>, <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">parallel_group</span></code>,
          <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span></code>, channels, and completion token
          adapters.
        </li>
<li class="listitem">
          Reverted the <code class="computeroutput"><span class="identifier">io_context</span></code>
          reference documentation to use <code class="computeroutput"><span class="identifier">executor_work_guard</span></code>
          when preventing the <code class="computeroutput"><span class="identifier">io_context</span></code>
          from running out of work.
        </li>
<li class="listitem">
          Removed references to <code class="computeroutput"><span class="identifier">deadline_timer</span></code>
          from the Overview documentation.
        </li>
<li class="listitem">
          Added reference documentation cross-references to asynchronous model elements.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h20"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_22_1"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_22_1">Asio
      1.22.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">bind_allocator</span></code>, to
          simplify associating a custom allocator with a completion token or handler.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">file_base</span><span class="special">::</span><span class="identifier">sync_all_on_write</span></code> flag, which maps to
          <code class="computeroutput"><span class="identifier">O_SYNC</span></code> on POSIX and <code class="computeroutput"><span class="identifier">FILE_FLAG_WRITE_THROUGH</span></code> on Windows.
        </li>
<li class="listitem">
          Added missing implementation of <code class="computeroutput"><span class="identifier">basic_file</span><span class="special">::</span><span class="identifier">release</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Added per-operation cancellation support to signal sets.
        </li>
<li class="listitem">
          Exposed <code class="computeroutput"><span class="identifier">recycling_allocator</span></code>
          as part of the public interface.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">nodiscard</span></code> attribute
          to the following functions:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                <code class="computeroutput"><span class="identifier">bind_allocator</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">bind_cancellation_slot</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">bind_executor</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">buffer</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">dynamic_buffer</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">append</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">as_single</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">as_tuple</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">make_parallel_group</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">prepend</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">get_associated_allocator</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">get_associated_cancellation_slot</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">get_associated_executor</span><span class="special">()</span></code>
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">make_work_guard</span><span class="special">()</span></code>
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added compatibility with OpenSSL 3.0, particularly when deprecated functionality
          is disabled.
        </li>
<li class="listitem">
          Added support for adopting an existing <code class="computeroutput"><span class="identifier">SSL</span><span class="special">*</span></code> into an <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code>.
        </li>
<li class="listitem">
          Enabled <code class="computeroutput"><span class="identifier">executor_work_guard</span><span class="special">&lt;&gt;</span></code> even when <code class="computeroutput"><span class="identifier">BOOST_ASIO_NO_TS_EXECUTORS</span></code>
          is defined.
        </li>
<li class="listitem">
          Enabled movable socket iostreams when using clang.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">bind_cancellation_slot</span></code>
          compatibility with legacy completion tokens.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">bind_executor</span></code> compatibility
          with legacy completion tokens.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">associator</span></code> specialisations
          for <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">append</span></code> and <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">prepend</span></code>,
          to correctly propagate the associated allocator, executor, and cancellation
          slot.
        </li>
<li class="listitem">
          Fixed 'zero as null pointer constant' warning in C++20 coroutines implementation
          of <code class="computeroutput"><span class="identifier">awaitable</span></code>.
        </li>
<li class="listitem">
          Ensured concurrency hint preprocessor macros are made available when <code class="literal">asio/io_context.hpp</code>
          is included.
        </li>
<li class="listitem">
          Fixed issue where the primary <code class="computeroutput"><span class="identifier">associated_allocator</span></code>
          template was not correctly detecting the nested <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">allocator_type</span></code>.
        </li>
<li class="listitem">
          Fixed <code class="literal">io_uring</code> implementation of <code class="computeroutput"><span class="identifier">async_receive_from</span></code>
          operation for sockets.
        </li>
<li class="listitem">
          Fixed <code class="literal">io_uring</code> implementation of <code class="computeroutput"><span class="identifier">write_some_at</span></code>
          operation for files.
        </li>
<li class="listitem">
          Changed <code class="literal">io_uring</code> implementation to correctly check that
          it is not the default before registering with reactor.
        </li>
<li class="listitem">
          Fixed a circular inclusion issue when using <code class="literal">io_uring</code>
          in some build configurations.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code>'s per-operation cancellation to
          clear the slot at completion of each operation.
        </li>
<li class="listitem">
          Fixed memory management in <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span></code>'s
          type-erased completion handlers.
        </li>
<li class="listitem">
          Fixed move <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span></code>
          implementation for <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span></code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">any_io_executor</span></code> implementation
          to work when both <code class="computeroutput"><span class="identifier">BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT</span></code>
          and <code class="computeroutput"><span class="identifier">BOOST_ASIO_SEPARATE_COMPILATION</span></code>
          are defined.
        </li>
<li class="listitem">
          Fixed implementation of <code class="computeroutput"><span class="identifier">basic_socket</span><span class="special">::</span><span class="identifier">at_mark</span><span class="special">()</span></code> when using the <code class="computeroutput"><span class="identifier">sockatmark</span><span class="special">()</span></code> system call.
        </li>
<li class="listitem">
          Changed the recycling allocator to use the default alignment as the minimum
          alignment for allocations.
        </li>
<li class="listitem">
          Added additional standard header file includes, as required by newer compilers.
        </li>
<li class="listitem">
          Added a workaround for apparent coroutine codegen bug with Apple's clang.
        </li>
<li class="listitem">
          Fixed various warnings in the examples and unit tests.
        </li>
<li class="listitem">
          Added a C++11 example showing file descriptor passing over local sockets.
          Thanks to Heiko Hund for providing this example.
        </li>
<li class="listitem">
          Added C++14 examples of wrapping callback-based APIs in asynchronous operations.
        </li>
<li class="listitem">
          Added an overview of Asio's asynchronous model to the documentation.
        </li>
<li class="listitem">
          Reworked reference documentation in terms of completion tokens.
        </li>
<li class="listitem">
          Updated documentation of asynchronous operation requirements to use new
          completion token form.
        </li>
<li class="listitem">
          Updated documentation for <code class="computeroutput"><span class="identifier">dispatch</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code>, and <code class="computeroutput"><span class="identifier">defer</span><span class="special">()</span></code> to cover both the old and new executor
          forms.
        </li>
<li class="listitem">
          Documented per-operation cancellation for serial ports.
        </li>
<li class="listitem">
          Clarified the non-concurrency guarantees made for allocators.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h21"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_22_0___boost_1_78"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_22_0___boost_1_78">Asio
      1.22.0 / Boost 1.78</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added an io_uring backend. This backend may be used for all I/O objects,
          including sockets, timers, and posix descriptors.<br> <br> The backend
          is disabled by default, and must be enabled by defining both <code class="computeroutput"><span class="identifier">BOOST_ASIO_HAS_IO_URING</span></code> and <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_EPOLL</span></code>.<br> <br>
          Simply defining <code class="computeroutput"><span class="identifier">BOOST_ASIO_HAS_IO_URING</span></code>
          alone will enable the backend without using it for the existing I/O objects.
          This allows it to be used for I/O objects that require io_uring support,
          such as files.<br> <br> This support depends on the <code class="literal">liburing</code>
          library at both compile and link time. Add <code class="computeroutput"><span class="special">-</span><span class="identifier">luring</span></code> to your list of libraries for
          linking.
        </li>
<li class="listitem">
<p class="simpara">
          Added support for files. This introduces new classes for stream-oriented
          and random-access files. For example, to write to a newly created stream-oriented
          file:<br>
        </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">stream_file</span> <span class="identifier">file</span><span class="special">(</span>
    <span class="identifier">my_io_context</span><span class="special">,</span> <span class="string">"/path/to/file"</span><span class="special">,</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">stream_file</span><span class="special">::</span><span class="identifier">write_only</span>
      <span class="special">|</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">stream_file</span><span class="special">::</span><span class="identifier">create</span>
      <span class="special">|</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">stream_file</span><span class="special">::</span><span class="identifier">truncate</span><span class="special">);</span>

<span class="identifier">file</span><span class="special">.</span><span class="identifier">async_write_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span>
    <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">});</span>
</pre>
<p class="simpara">
          <br> or to read from a random-access file:<br>
        </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">random_access_file</span> <span class="identifier">file</span><span class="special">(</span>
    <span class="identifier">my_io_context</span><span class="special">,</span> <span class="string">"/path/to/file"</span><span class="special">,</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">random_access_file</span><span class="special">::</span><span class="identifier">read_only</span><span class="special">);</span>

<span class="identifier">file</span><span class="special">.</span><span class="identifier">async_read_some_at</span><span class="special">(</span><span class="number">1234</span><span class="special">,</span> <span class="identifier">my_buffer</span><span class="special">,</span>
    <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">});</span>
</pre>
<p class="simpara">
          <br> This feature currently supports I/O completion ports on Windows,
          and io_uring on Linux (define <code class="computeroutput"><span class="identifier">BOOST_ASIO_HAS_IO_URING</span></code>
          to enable).
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added support for portable pipes. This change add supports for pipes on
          POSIX and Windows (when I/O completion ports are available). For example,
          to create and use a connected pair of pipe objects:<br>
        </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">readable_pipe</span> <span class="identifier">read_end</span><span class="special">;</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">writable_pipe</span> <span class="identifier">write_end</span><span class="special">;</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">connect_pipe</span><span class="special">(</span><span class="identifier">read_end</span><span class="special">,</span> <span class="identifier">write_end</span><span class="special">);</span>

<span class="identifier">write_end</span><span class="special">.</span><span class="identifier">async_write_some</span><span class="special">(</span><span class="identifier">my_write_buffer</span><span class="special">,</span>
    <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">});</span>

<span class="identifier">read_end</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_read_buffer</span><span class="special">,</span>
    <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">});</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added support for registered buffers. The <code class="computeroutput"><span class="identifier">mutable_registered_buffer</span></code>
          and <code class="computeroutput"><span class="identifier">const_registered_buffer</span></code>
          classes are buffer sequence types that represent registered buffers. These
          buffers are obtained by first performing a buffer registration:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">my_registration</span> <span class="special">=</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">register_buffers</span><span class="special">(</span>
      <span class="identifier">my_execution_context</span><span class="special">,</span>
      <span class="identifier">my_buffer_sequence</span><span class="special">);</span>
</pre>
<p class="simpara">
          <br> The registration object must be maintained for as long as the buffer
          registration is required. The supplied buffer sequence represents the memory
          location or locations that will be registered, and the caller must ensure
          they remain valid for as long as they are registered. The registration
          is automatically removed when the registration object is destroyed. There
          can be at most one active registration per execution context.<br> <br>
          The registration object is a container of registered buffers. Buffers may
          be obtained from it by iterating over the container, or via direct index
          access:<br>
        </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">mutable_registered_buffer</span> <span class="identifier">my_buffer</span>
  <span class="special">=</span> <span class="identifier">my_registration</span><span class="special">[</span><span class="identifier">i</span><span class="special">];</span>
</pre>
<p class="simpara">
          <br> The registered buffers may then be passed directly to operations:<br>
        </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_read</span><span class="special">(</span><span class="identifier">my_socket</span><span class="special">,</span> <span class="identifier">my_buffer</span><span class="special">,</span>
    <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">});</span>
</pre>
<p class="simpara">
          <br> Buffer registration supports the io_uring backend when used with
          read and write operations on descriptors, files, pipes, and sockets. For
          portability, the facility may be used on other platforms, but the registered
          buffers will behave as normal buffers.
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added experimental support for channels. This adds templates <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">basic_channel</span></code> and <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">basic_concurrent_channel</span></code>,
          with aliases <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">channel</span></code>
          and <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">concurrent_channel</span></code>. Channels may be used
          to send completions as messages. For example:<br>
        </p>
<pre class="programlisting"><span class="comment">// Create a channel with no buffer space.</span>
<span class="identifier">channel</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">(</span><span class="identifier">error_code</span><span class="special">,</span> <span class="identifier">size_t</span><span class="special">)&gt;</span> <span class="identifier">ch</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">);</span>

<span class="comment">// The call to try_send fails as there is no buffer</span>
<span class="comment">// space and no waiting receive operations.</span>
<span class="keyword">bool</span> <span class="identifier">ok</span> <span class="special">=</span> <span class="identifier">ch</span><span class="special">.</span><span class="identifier">try_send</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">eof</span><span class="special">,</span> <span class="number">123</span><span class="special">);</span>
<span class="identifier">assert</span><span class="special">(!</span><span class="identifier">ok</span><span class="special">);</span>

<span class="comment">// The async_send operation is outstanding until</span>
<span class="comment">// a receive operation consumes the message.</span>
<span class="identifier">ch</span><span class="special">.</span><span class="identifier">async_send</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">eof</span><span class="special">,</span> <span class="number">123</span><span class="special">,</span>
    <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">});</span>

<span class="comment">// The async_receive consumes the message. Both the</span>
<span class="comment">// async_send and async_receive operations complete</span>
<span class="comment">// immediately.</span>
<span class="identifier">ch</span><span class="special">.</span><span class="identifier">async_receive</span><span class="special">(</span>
    <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">});</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Implemented improvements to <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code>.
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Added overload so member functions can provide an explicit executor.
              </li>
<li class="listitem">
                Added <code class="computeroutput"><span class="identifier">co_spawn</span></code> for
                <code class="computeroutput"><span class="identifier">coro</span></code> tasks.
              </li>
<li class="listitem">
                Added reference and overview documentation.
              </li>
<li class="listitem">
                Adopted awaitable cancellation model.
              </li>
<li class="listitem">
                Refactored implementation.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Disabled <code class="computeroutput"><span class="identifier">aligned_alloc</span></code>
          on <code class="literal">clang</code> when using an MSVC runtime.
        </li>
<li class="listitem">
          Changed to use a faster implementation for <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">network_v4</span><span class="special">::</span><span class="identifier">canonical</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Added template specialisations for common uses to improve compile time.
        </li>
<li class="listitem">
          Reduced the size of <code class="computeroutput"><span class="identifier">io_context</span></code>
          executors to a single pointer.
        </li>
<li class="listitem">
          Increased the small object buffer size for <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">any_executor</span></code>
          and <code class="computeroutput"><span class="identifier">any_io_executor</span></code>.
        </li>
<li class="listitem">
          Fixed multi-signature handling when variadic templates are disabled.
        </li>
<li class="listitem">
          Fixed compatibility with new versions of <code class="literal">gcc</code> and <code class="literal">clang</code>.
        </li>
<li class="listitem">
          Fixed compilation on Solaris.
        </li>
<li class="listitem">
          Fixed defence against Qt-defined macros when building with MSVC.
        </li>
<li class="listitem">
          Improved error messages emitted by <code class="computeroutput"><span class="identifier">ssl</span></code>
          facilities.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">bind_executor</span></code> compatibility
          with completion tokens.
        </li>
<li class="listitem">
          Fixed build errors when <code class="computeroutput"><span class="identifier">BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT</span></code>
          is defined.
        </li>
<li class="listitem">
          Added missing move assignment operator to <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>.
        </li>
<li class="listitem">
          Fixed an access violation when using coroutines with MSVC, due to incorrect
          alignment of allocated memory.
        </li>
<li class="listitem">
          Fixed a cleanup issue in <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">parallel_group</span></code>
          that occured when the execution context was shut down with parallel operations
          still pending.
        </li>
<li class="listitem">
          Added clarifications to the documentation on concurrency hints.
        </li>
<li class="listitem">
          Added documentation on error handling techniques for C++20 coroutines.
        </li>
<li class="listitem">
          Fixed various warnings.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h22"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_20_0___boost_1_77"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_20_0___boost_1_77">Asio
      1.20.0 / Boost 1.77</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added support for cancellation of individual asynchronous operations. Cancellation
          is implemented by having each completion handler carry an associated <code class="computeroutput"><span class="identifier">CancellationSlot</span></code>, a lightweight cancellation
          channel that is specified through the new <code class="computeroutput"><span class="identifier">associated_cancellation_slot</span></code>
          associator. A concrete <code class="computeroutput"><span class="identifier">CancellationSlot</span></code>
          implementation is provided in the form of the <code class="computeroutput"><span class="identifier">cancellation_signal</span></code>
          and <code class="computeroutput"><span class="identifier">cancellation_slot</span></code> classes.
          In conjunction with the <code class="computeroutput"><span class="identifier">bind_cancellation_slot</span></code>
          helper function, these may be used to hook cancellation into asynchronous
          operations. However, it should be noted that these classes are the low-level
          building blocks of cancellation, and most use cases should use a higher
          level abstraction for cancellation, such as <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">parallel_group</span></code>
          or the new logical operators for <code class="computeroutput"><span class="identifier">awaitable</span></code>
          (see below). The ability to cancel individual operations, or composed operations,
          is currently supported by:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                timers
              </li>
<li class="listitem">
                sockets on POSIX and Windows
              </li>
<li class="listitem">
                POSIX descriptors
              </li>
<li class="listitem">
                Windows HANDLEs
              </li>
<li class="listitem">
                SSL streams
              </li>
<li class="listitem">
                all Asio-provided composed operations such as <code class="computeroutput"><span class="identifier">async_read</span></code>
                and <code class="computeroutput"><span class="identifier">async_write</span></code>
              </li>
<li class="listitem">
                compositions based on <code class="computeroutput"><span class="identifier">async_compose</span></code>
              </li>
<li class="listitem">
                C++20 coroutines that use <code class="computeroutput"><span class="identifier">awaitable</span></code>
              </li>
<li class="listitem">
                C++20 coroutines that use the new <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code>
                (see below)
              </li>
<li class="listitem">
                the new <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">parallel_group</span></code>
                operation (see below)
              </li>
<li class="listitem">
                the new <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span></code>
                class (see below)
              </li>
</ul></div>
        </li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">associator</span></code> trait.
          The <code class="computeroutput"><span class="identifier">associator</span></code> trait is
          used to generically forward associators, such as <code class="computeroutput"><span class="identifier">associated_executor</span></code>
          and <code class="computeroutput"><span class="identifier">associated_allocator</span></code>,
          through intermediate completion handlers. For example:<br>
        </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Handler</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">intermediate_handler</span>
<span class="special">{</span>
  <span class="identifier">Handler</span> <span class="identifier">handler_</span><span class="special">;</span>

  <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span>
  <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">Args</span><span class="special">&amp;...</span> <span class="identifier">args</span><span class="special">)</span>
  <span class="special">{</span>
    <span class="comment">// ...</span>
  <span class="special">}</span>
<span class="special">};</span>

<span class="keyword">namespace</span> <span class="identifier">asio</span> <span class="special">{</span>
  <span class="keyword">template</span> <span class="special">&lt;</span>
      <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span><span class="special">,</span> <span class="keyword">typename</span><span class="special">&gt;</span> <span class="keyword">class</span> <span class="identifier">Associator</span><span class="special">,</span>
      <span class="keyword">typename</span> <span class="identifier">Handler</span><span class="special">,</span>
      <span class="keyword">typename</span> <span class="identifier">DefaultCandidate</span><span class="special">&gt;</span>
  <span class="keyword">struct</span> <span class="identifier">associator</span><span class="special">&lt;</span>
      <span class="identifier">Associator</span><span class="special">,</span>
      <span class="identifier">intermediate_handler</span><span class="special">&lt;</span><span class="identifier">Handler</span><span class="special">&gt;,</span>
      <span class="identifier">DefaultCandidate</span><span class="special">&gt;</span>
  <span class="special">{</span>
    <span class="keyword">using</span> <span class="identifier">type</span> <span class="special">=</span>
      <span class="keyword">typename</span> <span class="identifier">Associator</span><span class="special">&lt;</span><span class="identifier">Handler</span><span class="special">,</span> <span class="identifier">DefaultCandidate</span><span class="special">&gt;::</span><span class="identifier">type</span><span class="special">;</span>

    <span class="keyword">static</span> <span class="identifier">type</span> <span class="identifier">get</span><span class="special">(</span>
        <span class="keyword">const</span> <span class="identifier">intermediate_handler</span><span class="special">&lt;</span><span class="identifier">Handler</span><span class="special">&gt;&amp;</span> <span class="identifier">h</span><span class="special">,</span>
        <span class="keyword">const</span> <span class="identifier">DefaultCandidate</span><span class="special">&amp;</span> <span class="identifier">c</span> <span class="special">=</span> <span class="identifier">DefaultCandidate</span><span class="special">())</span> <span class="keyword">noexcept</span>
    <span class="special">{</span>
      <span class="keyword">return</span> <span class="identifier">Associator</span><span class="special">&lt;</span><span class="identifier">Handler</span><span class="special">,</span> <span class="identifier">DefaultCandidate</span><span class="special">&gt;::</span><span class="identifier">get</span><span class="special">(</span>
          <span class="identifier">h</span><span class="special">.</span><span class="identifier">handler_</span><span class="special">,</span> <span class="identifier">c</span><span class="special">);</span>
    <span class="special">}</span>
  <span class="special">};</span>
<span class="special">}</span> <span class="comment">// namespace asio</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Changed all asynchronous operations implemented in Asio to invoke their
          completion handlers as rvalue references. This allows an rvalue reference
          qualifier to be added to the function call operator.
        </li>
<li class="listitem">
<p class="simpara">
          Added support for asynchronous operations with multiple completion signatures.
          Completion signatures may also specify that they are <code class="computeroutput"><span class="keyword">noexcept</span></code>,
          and whether they are lvalue-invocable (and thus do not "consume"
          the completion handler) or rvalue-invocable (and thus do "consume"
          the handler, indicating an end to the asynchronous operation). For example:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">my_async_operation</span><span class="special">(...,</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">completion_token_for</span><span class="special">&lt;</span>
      <span class="keyword">void</span><span class="special">(</span><span class="identifier">intermediate_result_type</span><span class="special">)</span> <span class="special">&amp;</span> <span class="keyword">noexcept</span><span class="special">,</span>
      <span class="keyword">void</span><span class="special">(</span><span class="identifier">final_result_type</span><span class="special">)</span> <span class="special">&amp;&amp;</span>
    <span class="special">&gt;</span> <span class="keyword">auto</span><span class="special">&amp;&amp;</span> <span class="identifier">token</span><span class="special">)</span>
<span class="special">{</span>
  <span class="comment">// ...</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added <code class="computeroutput"><span class="keyword">operator</span><span class="special">&amp;&amp;</span></code>
          and <code class="computeroutput"><span class="keyword">operator</span><span class="special">||</span></code>
          for <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>.
          The logical operators <code class="computeroutput"><span class="special">||</span></code> and
          <code class="computeroutput"><span class="special">&amp;&amp;</span></code> have been overloaded
          for <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>,
          to allow coroutines to be trivially awaited in parallel.<br> <br> When
          awaited using <code class="computeroutput"><span class="special">&amp;&amp;</span></code>,
          the <code class="computeroutput"><span class="identifier">co_await</span></code> expression
          waits until both operations have completed successfully. As a "short-circuit"
          evaluation, if one operation fails with an exception, the other is immediately
          cancelled. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">results</span> <span class="special">=</span>
  <span class="identifier">co_await</span> <span class="special">(</span>
    <span class="identifier">async_read</span><span class="special">(</span><span class="identifier">socket</span><span class="special">,</span> <span class="identifier">input_buffer</span><span class="special">,</span> <span class="identifier">use_awaitable</span><span class="special">)</span>
      <span class="special">&amp;&amp;</span> <span class="identifier">async_write</span><span class="special">(</span><span class="identifier">socket</span><span class="special">,</span> <span class="identifier">output_buffer</span><span class="special">,</span> <span class="identifier">use_awaitable</span><span class="special">)</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br> When awaited using <code class="computeroutput"><span class="special">||</span></code>,
          the <code class="computeroutput"><span class="identifier">co_await</span></code> expression
          waits until either operation succeeds. As a "short-circuit" evaluation,
          if one operation succeeds without throwing an exception, the other is immediately
          cancelled. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">monostate</span><span class="special">&gt;</span> <span class="identifier">results</span> <span class="special">=</span>
  <span class="identifier">co_await</span> <span class="special">(</span>
    <span class="identifier">async_read</span><span class="special">(</span><span class="identifier">socket</span><span class="special">,</span> <span class="identifier">input_buffer</span><span class="special">,</span> <span class="identifier">use_awaitable</span><span class="special">)</span>
      <span class="special">||</span> <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">use_awaitable</span><span class="special">)</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br> The operators may be enabled by adding the <code class="computeroutput"><span class="preprocessor">#include</span></code>:<br>
        </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">asio</span><span class="special">/</span><span class="identifier">experimental</span><span class="special">/</span><span class="identifier">awaitable_operators</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<p class="simpara">
          <br> and then bringing the contents of the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">awaitable_operators</span></code>
          namespace into scope:<br>
        </p>
<pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">awaitable_operators</span><span class="special">;</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">as_tuple</span></code>
          completion token adapter. The <code class="computeroutput"><span class="identifier">as_tuple</span></code>
          completion token adapter can be used to specify that the completion handler
          arguments should be combined into a single tuple argument. The <code class="computeroutput"><span class="identifier">as_tuple</span></code> adapter may be used in conjunction
          with <code class="computeroutput"><span class="identifier">use_awaitable</span></code> and
          structured bindings as follows:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="special">[</span><span class="identifier">e</span><span class="special">,</span> <span class="identifier">n</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">),</span> <span class="identifier">as_tuple</span><span class="special">(</span><span class="identifier">use_awaitable</span><span class="special">));</span>
</pre>
<p class="simpara">
          <br> Alternatively, it may be used as a default completion token like
          so:<br>
        </p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">default_token</span> <span class="special">=</span> <span class="identifier">as_tuple_t</span><span class="special">&lt;</span><span class="identifier">use_awaitable_t</span><span class="special">&lt;&gt;&gt;;</span>
<span class="keyword">using</span> <span class="identifier">tcp_socket</span> <span class="special">=</span> <span class="identifier">default_token</span><span class="special">::</span><span class="identifier">as_default_on_t</span><span class="special">&lt;</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&gt;;</span>
<span class="comment">// ...</span>
<span class="identifier">awaitable</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">do_read</span><span class="special">(</span><span class="identifier">tcp_socket</span> <span class="identifier">socket</span><span class="special">)</span>
<span class="special">{</span>
  <span class="comment">// ...</span>
  <span class="keyword">auto</span> <span class="special">[</span><span class="identifier">e</span><span class="special">,</span> <span class="identifier">n</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">));</span>
  <span class="comment">// ...</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">append</span></code>
          completion token adapter. The <code class="computeroutput"><span class="identifier">append</span></code>
          completion token adapter can be used to pass additional completion handler
          arguments at the end of the completion signature. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">append</span><span class="special">(</span>
      <span class="special">[](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">i</span><span class="special">)</span>
      <span class="special">{</span>
        <span class="comment">// ...</span>
      <span class="special">},</span>
    <span class="number">42</span><span class="special">)</span>
  <span class="special">);</span>

<span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">f</span> <span class="special">=</span> <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">append</span><span class="special">(</span>
      <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span><span class="special">,</span>
      <span class="number">42</span>
    <span class="special">)</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">prepend</span></code>
          completion token adapter. The <code class="computeroutput"><span class="identifier">prepend</span></code>
          completion token adapter can be used to pass additional arguments before
          the existing completion handler arguments. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">prepend</span><span class="special">(</span>
      <span class="special">[](</span><span class="keyword">int</span> <span class="identifier">i</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">)</span>
      <span class="special">{</span>
        <span class="comment">// ...</span>
      <span class="special">},</span>
    <span class="number">42</span><span class="special">)</span>
  <span class="special">);</span>

<span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&gt;&gt;</span> <span class="identifier">f</span> <span class="special">=</span> <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">prepend</span><span class="special">(</span>
      <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span><span class="special">,</span>
      <span class="number">42</span>
    <span class="special">)</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">deferred</span></code>
          completion token. The <code class="computeroutput"><span class="identifier">deferred</span></code>
          completion token takes a call to an asynchronous operation's initiating
          function and turns it into a function object that accepts a completion
          token. For example:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">deferred_op</span> <span class="special">=</span>
  <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">);</span>
<span class="special">...</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">deferred_op</span><span class="special">)(</span>
    <span class="special">[](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">){</span> <span class="special">...</span> <span class="special">});</span>
</pre>
<p class="simpara">
          <br> or:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">deferred_op</span> <span class="special">=</span>
  <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">);</span>
<span class="special">...</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="special">=</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">deferred_op</span><span class="special">)(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span><span class="special">);</span>
</pre>
<p class="simpara">
          <br> The deferred token also supports chaining, to create simple compositions:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">deferred_op</span> <span class="special">=</span>
  <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">(</span>
      <span class="special">[&amp;](</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">)</span>
      <span class="special">{</span>
        <span class="identifier">timer</span><span class="special">.</span><span class="identifier">expires_after</span><span class="special">(</span>
            <span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>

        <span class="keyword">return</span> <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
            <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">);</span>
      <span class="special">});</span>
<span class="special">...</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">deferred_op</span><span class="special">)(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span><span class="special">);</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">parallel_group</span></code>
          class and <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">make_parallel_group</span></code>
          function. This utility may be used to launch work that is performed in
          parallel, and wait for one or all of the operations to complete. A <code class="computeroutput"><span class="identifier">parallel_group</span></code> implements automatic cancellation
          of incomplete operations. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">make_parallel_group</span><span class="special">(</span>
    <span class="special">[&amp;](</span><span class="keyword">auto</span> <span class="identifier">token</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="keyword">return</span> <span class="identifier">stream</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">),</span> <span class="identifier">token</span><span class="special">);</span>
    <span class="special">},</span>
    <span class="special">[&amp;](</span><span class="keyword">auto</span> <span class="identifier">token</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="keyword">return</span> <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">token</span><span class="special">);</span>
    <span class="special">}</span>
  <span class="special">).</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">experimental</span><span class="special">::</span><span class="identifier">wait_for_one</span><span class="special">(),</span>
    <span class="special">[](</span>
        <span class="identifier">std</span><span class="special">::</span><span class="identifier">array</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">,</span> <span class="number">2</span><span class="special">&gt;</span> <span class="identifier">completion_order</span><span class="special">,</span>
        <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec1</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n1</span><span class="special">,</span>
        <span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec2</span>
    <span class="special">)</span>
    <span class="special">{</span>
      <span class="comment">// ...</span>
    <span class="special">}</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br> The conditions for completion of the group may be specified using
          one of the four provided function objects <code class="computeroutput"><span class="identifier">wait_for_all</span></code>,
          <code class="computeroutput"><span class="identifier">wait_for_one</span></code>, <code class="computeroutput"><span class="identifier">wait_for_one_success</span></code>, and <code class="computeroutput"><span class="identifier">wait_for_one_error</span></code>, or with a custom
          function. The <code class="computeroutput"><span class="identifier">parallel_group</span></code>
          class can also be combined with <code class="computeroutput"><span class="identifier">deferred</span></code>
          as follows:<br>
        </p>
<pre class="programlisting"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">make_parallel_group</span><span class="special">(</span>
    <span class="identifier">stream</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">),</span> <span class="identifier">experimental</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">),</span>
    <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">deferred</span><span class="special">)</span>
  <span class="special">).</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="comment">// ...</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br> Note: for maximum flexibility, <code class="computeroutput"><span class="identifier">parallel_group</span></code>
          does not propagate the executor automatically to the operations within
          the group.
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span></code>. The <code class="computeroutput"><span class="identifier">promise</span></code>
          type allows eager execution and synchronisation of async operations. For
          example:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">promise</span> <span class="special">=</span> <span class="identifier">async_read</span><span class="special">(</span>
    <span class="identifier">stream</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">),</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">use_promise</span><span class="special">);</span>

<span class="special">...</span> <span class="keyword">do</span> <span class="identifier">other</span> <span class="identifier">stuff</span> <span class="keyword">while</span> <span class="identifier">the</span> <span class="identifier">read</span> <span class="identifier">is</span> <span class="identifier">going</span> <span class="identifier">on</span> <span class="special">...</span>

<span class="identifier">promise</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span> <span class="comment">// completion the operation</span>
    <span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_read</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="special">...</span>
    <span class="special">});</span>
</pre>
<p class="simpara">
          <br> Promises can be safely disregarded if the result is no longer required.
          Different operations can be combined to either wait for all to complete
          or for one to complete (and cancel the rest). For example, to wait for
          one to complete:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">timeout_promise</span> <span class="special">=</span>
  <span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">use_promise</span><span class="special">);</span>

<span class="keyword">auto</span> <span class="identifier">read_promise</span> <span class="special">=</span> <span class="identifier">async_read</span><span class="special">(</span>
    <span class="identifier">stream</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">),</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">use_promise</span><span class="special">);</span>

<span class="keyword">auto</span> <span class="identifier">promise</span> <span class="special">=</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span><span class="special">&lt;&gt;::</span><span class="identifier">race</span><span class="special">(</span>
    <span class="identifier">timeout_promise</span><span class="special">,</span> <span class="identifier">read_promise</span><span class="special">);</span>

<span class="identifier">promise</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="special">[](</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;</span><span class="identifier">error_code</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span><span class="identifier">error_code</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;&gt;</span> <span class="identifier">v</span><span class="special">)</span>
    <span class="special">{</span>
      <span class="keyword">if</span> <span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">index</span><span class="special">()</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> <span class="special">{}</span> <span class="comment">//timed out</span>
      <span class="keyword">else</span> <span class="keyword">if</span> <span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">index</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">)</span> <span class="comment">// completed in time</span>
    <span class="special">});</span>
</pre>
<p class="simpara">
          <br> or to wait for all to complete:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">write_promise</span> <span class="special">=</span> <span class="identifier">async_write</span><span class="special">(</span>
    <span class="identifier">stream</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">my_write_buffer</span><span class="special">),</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">use_promise</span><span class="special">);</span>

<span class="keyword">auto</span> <span class="identifier">read_promise</span> <span class="special">=</span> <span class="identifier">async_read</span><span class="special">(</span>
    <span class="identifier">stream</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">),</span>
    <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">use_promise</span><span class="special">);</span>

<span class="keyword">auto</span> <span class="identifier">promise</span> <span class="special">=</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">promise</span><span class="special">&lt;&gt;::</span><span class="identifier">all</span><span class="special">(</span>
    <span class="identifier">write_promise</span><span class="special">,</span> <span class="identifier">read_promise</span><span class="special">);</span>

<span class="identifier">promise</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span>
    <span class="special">[](</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span><span class="identifier">error_code</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">write_result</span><span class="special">,</span>
      <span class="identifier">std</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span><span class="identifier">error_code</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span class="special">&gt;</span> <span class="identifier">read_result</span><span class="special">)</span>
    <span class="special">{</span>
    <span class="special">});</span>
</pre>
<p class="simpara">
          <br> Thanks go to Klemens Morgenstern for contributing this feature.
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span></code>
          class template. The <code class="computeroutput"><span class="identifier">coro</span></code>
          type is a C++20 coroutine primitive for resumable functions, with the ability
          to combine both asynchronous waiting (<code class="computeroutput"><span class="identifier">co_await</span></code>)
          and yielding (<code class="computeroutput"><span class="identifier">co_yield</span></code>)
          into a single, stateful control flow. For example:<br>
        </p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">asio</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">asio</span><span class="special">/</span><span class="identifier">experimental</span><span class="special">/</span><span class="identifier">coro</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>

<span class="keyword">using</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">;</span>

<span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">coro</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="identifier">reader</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">sock</span><span class="special">)</span>
<span class="special">{</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">buf</span><span class="special">;</span>
  <span class="keyword">while</span> <span class="special">(</span><span class="identifier">sock</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">())</span>
  <span class="special">{</span>
    <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">n</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">async_read_until</span><span class="special">(</span>
        <span class="identifier">sock</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">dynamic_buffer</span><span class="special">(</span><span class="identifier">buf</span><span class="special">),</span> <span class="char">'\n'</span><span class="special">,</span>
        <span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">use_coro</span><span class="special">);</span>
    <span class="identifier">co_yield</span> <span class="identifier">buf</span><span class="special">.</span><span class="identifier">substr</span><span class="special">(</span><span class="number">0</span><span class="special">,</span> <span class="identifier">n</span><span class="special">);</span>
    <span class="identifier">buf</span><span class="special">.</span><span class="identifier">erase</span><span class="special">(</span><span class="number">0</span><span class="special">,</span> <span class="identifier">n</span><span class="special">);</span>
  <span class="special">}</span>
<span class="special">}</span>

<span class="identifier">asio</span><span class="special">::</span><span class="identifier">awaitable</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">consumer</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">sock</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">auto</span> <span class="identifier">r</span> <span class="special">=</span> <span class="identifier">reader</span><span class="special">(</span><span class="identifier">sock</span><span class="special">);</span>
  <span class="keyword">auto</span> <span class="identifier">msg1</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">r</span><span class="special">.</span><span class="identifier">async_resume</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_awaitable</span><span class="special">);</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Message 1: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">msg1</span><span class="special">.</span><span class="identifier">value_or</span><span class="special">(</span><span class="string">"\n"</span><span class="special">);</span>
  <span class="keyword">auto</span> <span class="identifier">msg2</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">r</span><span class="special">.</span><span class="identifier">async_resume</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_awaitable</span><span class="special">);</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Message 2: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">msg2</span><span class="special">.</span><span class="identifier">value_or</span><span class="special">(</span><span class="string">"\n"</span><span class="special">);</span>
<span class="special">}</span>

<span class="identifier">asio</span><span class="special">::</span><span class="identifier">awaitable</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">listen</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">acceptor</span><span class="special">&amp;</span> <span class="identifier">acceptor</span><span class="special">)</span>
<span class="special">{</span>
  <span class="keyword">for</span> <span class="special">(;;)</span>
  <span class="special">{</span>
    <span class="identifier">co_spawn</span><span class="special">(</span>
        <span class="identifier">acceptor</span><span class="special">.</span><span class="identifier">get_executor</span><span class="special">(),</span>
        <span class="identifier">consumer</span><span class="special">(</span><span class="identifier">co_await</span> <span class="identifier">acceptor</span><span class="special">.</span><span class="identifier">async_accept</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_awaitable</span><span class="special">)),</span>
        <span class="identifier">asio</span><span class="special">::</span><span class="identifier">detached</span><span class="special">);</span>
  <span class="special">}</span>
<span class="special">}</span>

<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span> <span class="identifier">ctx</span><span class="special">;</span>
  <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">acceptor</span> <span class="identifier">acceptor</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span> <span class="special">{</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">v4</span><span class="special">(),</span> <span class="number">54321</span><span class="special">});</span>
  <span class="identifier">co_spawn</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">,</span> <span class="identifier">listen</span><span class="special">(</span><span class="identifier">acceptor</span><span class="special">),</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">detached</span><span class="special">);</span>
  <span class="identifier">ctx</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          <br> Thanks go to Klemens Morgenstern for contributing this feature.
        </p>
</li>
<li class="listitem">
          Added move assignment to <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code>.
        </li>
<li class="listitem">
          Changed <code class="computeroutput"><span class="identifier">co_spawn</span></code> to <code class="computeroutput"><span class="identifier">dispatch</span></code> the coroutine's initial step
          to the executor, and to only <code class="computeroutput"><span class="identifier">post</span></code>
          the completion handler if the coroutine did not otherwise perform a context
          switch (i.e. a <code class="computeroutput"><span class="identifier">co_await</span></code>
          on an asynchronous operation).
        </li>
<li class="listitem">
          Enabled additional optimisations for <code class="computeroutput"><span class="identifier">any_executor</span></code>
          and <code class="computeroutput"><span class="identifier">any_io_executor</span></code> when
          used with asynchronous operations.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">nodiscard</span></code> attribute
          to <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>.
        </li>
<li class="listitem">
          Increased the number of cached slots in the default recycling allocator.
          This number defaults to 2, but may also be specified by defining the <code class="computeroutput"><span class="identifier">BOOST_ASIO_RECYCLING_ALLOCATOR_CACHE_SIZE</span></code>
          macro.
        </li>
<li class="listitem">
          Disabled the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">system_error</span></code> message workaround for recent
          MSVC.
        </li>
<li class="listitem">
          Changed the default allocator behaviour to respect alignment requirements,
          to support over-aligned types. Requires C++17 or later, or Boost.
        </li>
<li class="listitem">
          Ensured the result strings are always initialised in reverse name resolution.
        </li>
<li class="listitem">
          Fixed recursive template instantiation issues in <code class="computeroutput"><span class="identifier">use_awaitable_t</span><span class="special">::</span><span class="identifier">executor_with_default</span></code>.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">any_io_executor</span></code>
          equality operators to correctly return a result based on the target executor.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">strand</span><span class="special">&lt;&gt;</span></code>
          to avoid using a potentially moved-from executor.
        </li>
<li class="listitem">
          Ensured <code class="literal">gcc</code> tests are not used for <code class="literal">clang</code>
          when detecting compiler features.
        </li>
<li class="listitem">
          Disabled coroutines support for the <code class="literal">clang</code> shipped with
          MSVC.
        </li>
<li class="listitem">
          Fixed compatibility with recent LibreSSL when <code class="computeroutput"><span class="identifier">OPENSSL_NO_SSL_INTERN</span></code>
          is defined.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">posix</span><span class="special">::</span><span class="identifier">basic_stream_descriptor</span></code> move operations
          to work with non-defaulted executors.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h23"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_18_2___boost_1_76"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_18_2___boost_1_76">Asio
      1.18.2 / Boost 1.76</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">scope_id_type</span></code> type alias.
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">port_type</span></code> type alias.
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">hash</span></code> specialisations for IP addresses.
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">hash</span></code> specialisations for <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">basic_endpoint</span><span class="special">&lt;&gt;</span></code>.
        </li>
<li class="listitem">
          Refactored SFINAE usage to improve compile times.
        </li>
<li class="listitem">
          Added friendship support to customisation points, and made most customisations
          private.
        </li>
<li class="listitem">
          Changed <code class="computeroutput"><span class="identifier">any_io_executor</span></code>
          to a "strong typedef"-style class.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">as_single</span></code> to work with handler hook deprecation.
        </li>
<li class="listitem">
          Ensured pthread condition variable attributes are cleaned up on all platforms.
        </li>
<li class="listitem">
          Clarified thread safety notes on sockets and descriptors.
        </li>
<li class="listitem">
          Ensured <code class="computeroutput"><span class="identifier">errno</span></code> is not overwritten
          if <code class="computeroutput"><span class="identifier">socket</span><span class="special">()</span></code>
          fails on macOS/FreeBSD.
        </li>
<li class="listitem">
          Fixed work tracking for <code class="computeroutput"><span class="identifier">io_context</span></code>
          and <code class="computeroutput"><span class="identifier">thread_pool</span></code> executors
          when move-assigned.
        </li>
<li class="listitem">
          Ensured internal <code class="computeroutput"><span class="identifier">call_stack</span></code>
          objects are accessed only from implementation files.
        </li>
<li class="listitem">
          Fixed I/O object move-assignment to ensure the executor is left in a valid
          state.
        </li>
<li class="listitem">
          Fixed detection of compiler support for defaulted template argument on
          functions with MSVC.
        </li>
<li class="listitem">
          Prevented the <code class="computeroutput"><span class="identifier">blocking</span><span class="special">.</span><span class="identifier">always</span></code>
          property from being used with <code class="computeroutput"><span class="identifier">strand</span><span class="special">&lt;&gt;</span></code>, as it did not produce the correct
          semantics.
        </li>
<li class="listitem">
          Removed deprecated file <code class="literal">asio/impl/src.cpp</code>.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h24"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_18_1___boost_1_75"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_18_1___boost_1_75">Asio
      1.18.1 / Boost 1.75</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Enabled support for UNIX domain sockets on Windows. From Windows 10, UNIX
          domain sockets (a.k.a "local" sockets) are supported on Windows,
          with the exception of the <code class="computeroutput"><span class="identifier">connect_pair</span></code>
          function (which will fail with an operation_not_supported error).
        </li>
<li class="listitem">
          Added executor-converting construction and assignment to <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">basic_resolver</span></code>.
        </li>
<li class="listitem">
          Added compatibility between polymorphic executors and the (deprecated)
          handler invocation hook.
        </li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">as_single</span></code>
          completion token adapter. The <code class="computeroutput"><span class="identifier">as_single</span></code>
          completion token adapter can be used to specify that the completion handler
          arguments should be combined into a single argument. For completion signatures
          with a single parameter, the argument is passed through as-is. For signatures
          with two or more parameters, the arguments are combined into a tuple. The
          <code class="computeroutput"><span class="identifier">as_single</span></code> adapter may be
          used in conjunction with <code class="computeroutput"><span class="identifier">use_awaitable</span></code>
          and structured bindings as follows:<br>
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="special">[</span><span class="identifier">e</span><span class="special">,</span> <span class="identifier">n</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span>
    <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">),</span> <span class="identifier">as_single</span><span class="special">(</span><span class="identifier">use_awaitable</span><span class="special">));</span>
</pre>
<p class="simpara">
          <br> Alternatively, it may be used as a default completion token like
          so:<br>
        </p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">default_token</span> <span class="special">=</span> <span class="identifier">as_single_t</span><span class="special">&lt;</span><span class="identifier">use_awaitable_t</span><span class="special">&lt;&gt;&gt;;</span>
<span class="keyword">using</span> <span class="identifier">tcp_socket</span> <span class="special">=</span> <span class="identifier">default_token</span><span class="special">::</span><span class="identifier">as_default_on_t</span><span class="special">&lt;</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&gt;;</span>
<span class="comment">// ...</span>
<span class="identifier">awaitable</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span> <span class="identifier">do_read</span><span class="special">(</span><span class="identifier">tcp_socket</span> <span class="identifier">socket</span><span class="special">)</span>
<span class="special">{</span>
  <span class="comment">// ...</span>
  <span class="keyword">auto</span> <span class="special">[</span><span class="identifier">e</span><span class="special">,</span> <span class="identifier">n</span><span class="special">]</span> <span class="special">=</span> <span class="identifier">co_await</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span class="identifier">data</span><span class="special">));</span>
  <span class="comment">// ...</span>
<span class="special">}</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Added support for <code class="computeroutput"><span class="identifier">MSG_NOSIGNAL</span></code>
          on more platforms by using <code class="computeroutput"><span class="identifier">_POSIX_VERSION</span></code>
          to detect whether it is supported.
        </li>
<li class="listitem">
          Added the ability to compile using libpthread on Windows.
        </li>
<li class="listitem">
          Added workarounds for the Intel C++ compiler.
        </li>
<li class="listitem">
          Added more support for detecting and optimising for handlers that have
          no custom executor.
        </li>
<li class="listitem">
          Reduced lock contention for timer cancellation on Windows.
        </li>
<li class="listitem">
          Reinstated a previously removed null-pointer check, as it had a measurable
          impact on performance.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">executor</span></code> concept
          to test for a const-qualified <code class="computeroutput"><span class="identifier">execute</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">any_executor</span></code> support
          for builds without RTTI support.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">thread_pool</span></code> unit
          test to work without RTTI support.
        </li>
<li class="listitem">
          Fixed C++20 coroutines compatibility with clang on Windows.
        </li>
<li class="listitem">
          Fixed some compatibility issues with Windows Runtime.
        </li>
<li class="listitem">
          Fixed shadow name warnings caused by addition of <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">query</span></code>.
        </li>
<li class="listitem">
          Fixed a "logical ‘or’ of equal expressions" warning on linux.
        </li>
<li class="listitem">
          Fixed a benign switch fallthrough warning.
        </li>
<li class="listitem">
          Added missing <code class="computeroutput"><span class="identifier">push</span><span class="special">/</span><span class="identifier">pop_options</span><span class="special">.</span><span class="identifier">hpp</span></code> includes.
        </li>
<li class="listitem">
          Suppressed zero-as-null-pointer-constant warnings.
        </li>
<li class="listitem">
          Fixed a comma-operator warning.
        </li>
<li class="listitem">
          Updated the documentation to clarify when the <code class="literal">select</code>
          reactor is used on Windows.
        </li>
<li class="listitem">
          Fixed potential ambiguity caused by <code class="computeroutput"><span class="identifier">any_executor</span></code>
          comparisons and conversion.
        </li>
<li class="listitem">
          Added detection of non-experimental C++20 coroutines on MSVC 19.8.
        </li>
<li class="listitem">
          Fixed compatibility with uClibc.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">strand</span><span class="special">&lt;&gt;</span></code>
          adaptation of Networking TS executors when targeting older C++ versions
          or less conformant compilers.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h25"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_18_0___boost_1_74"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_18_0___boost_1_74">Asio
      1.18.0 / Boost 1.74</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added an implementation of the proposed standard executors (<a href="http://wg21.link/P0443r13" target="_top">P0443r13</a>,
          <a href="http://wg21.link/P1348r0" target="_top">P1348r0</a>, and <a href="http://wg21.link/P1393r0" target="_top">P1393r0</a>).
        </li>
<li class="listitem">
          Added support for the proposed standard executors to Asio's I/O facilities:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                The <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">executor_type</span></code>, <code class="computeroutput"><span class="identifier">thread_pool</span><span class="special">::</span><span class="identifier">executor_type</span></code>,
                <code class="computeroutput"><span class="identifier">system_executor</span></code>,
                and <code class="computeroutput"><span class="identifier">strand</span></code> executors
                now meet the requirements for the proposed standard executors. These
                classes also continue to meet the existing requirements for the Networking
                TS model of executors.
              </li>
<li class="listitem">
                All I/O objects, asynchronous operations, and utilities including
                <code class="computeroutput"><span class="identifier">dispatch</span></code>, <code class="computeroutput"><span class="identifier">post</span></code>, <code class="computeroutput"><span class="identifier">defer</span></code>,
                <code class="computeroutput"><span class="identifier">get_associated_executor</span></code>,
                <code class="computeroutput"><span class="identifier">bind_executor</span></code>, <code class="computeroutput"><span class="identifier">make_work_guard</span></code>, <code class="computeroutput"><span class="identifier">spawn</span></code>, <code class="computeroutput"><span class="identifier">co_spawn</span></code>,
                <code class="computeroutput"><span class="identifier">async_compose</span></code>, <code class="computeroutput"><span class="identifier">use_future</span></code>, etc., can interoperate
                with both new proposed standard executors, and with existing Networking
                TS executors. The implementation determines at compile time which
                model a particular executor meets; the proposed standard executor
                model is used in preference if both are detected.
              </li>
<li class="listitem">
                The <code class="computeroutput"><span class="identifier">any_io_executor</span></code>
                type alias has been introduced as the new default runtime-polymorphic
                executor for all I/O objects. This type alias points to the <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">any_executor</span><span class="special">&lt;&gt;</span></code>
                template with a set of supportable properties specified for use with
                I/O. This change may break existing code that directly uses the old
                polymorphic wrapper, <code class="computeroutput"><span class="identifier">executor</span></code>.
                If required for backward compatibility, <code class="computeroutput"><span class="identifier">BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT</span></code>
                can be defined, which changes the <code class="computeroutput"><span class="identifier">any_io_executor</span></code>
                type alias to instead point to the <code class="computeroutput"><span class="identifier">executor</span></code>
                polymorphic wrapper.
              </li>
<li class="listitem">
                Support for the existing Networking TS model of executors can be
                disabled by defining <code class="computeroutput"><span class="identifier">BOOST_ASIO_NO_TS_EXECUTORS</span></code>.
              </li>
</ul></div>
        </li>
<li class="listitem">
<p class="simpara">
          Added converting move construction and assignment to <code class="computeroutput"><span class="identifier">basic_waitable_timer</span></code>.
          This enables move construction and assignment between different timer types,
          provided the executor types are convertible. For example:<br>
        </p>
<pre class="programlisting"><span class="identifier">basic_waitable_timer</span><span class="special">&lt;</span>
    <span class="identifier">clock_type</span><span class="special">,</span>
    <span class="identifier">traits_type</span><span class="special">,</span>
    <span class="identifier">io_context</span><span class="special">::</span><span class="identifier">executor_type</span>
  <span class="special">&gt;</span> <span class="identifier">timer1</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>

<span class="identifier">basic_waitable_timer</span><span class="special">&lt;</span>
    <span class="identifier">clock_type</span><span class="special">,</span>
    <span class="identifier">traits_type</span><span class="special">,</span>
    <span class="identifier">any_io_executor</span> <span class="comment">// polymorphic wrapper</span>
  <span class="special">&gt;</span> <span class="identifier">timer2</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">timer1</span><span class="special">));</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Enabled C++20 coroutine support when using <code class="literal">gcc</code> 10.
        </li>
<li class="listitem">
<p class="simpara">
          Added overloads of <code class="computeroutput"><span class="identifier">co_spawn</span></code>
          that launch an awaitable. This change allows us to write:<br>
        </p>
<pre class="programlisting"><span class="identifier">co_spawn</span><span class="special">(</span><span class="identifier">executor</span><span class="special">,</span>
    <span class="identifier">echo</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">socket</span><span class="special">)),</span>
    <span class="identifier">detached</span><span class="special">);</span>
</pre>
<p class="simpara">
          <br> instead of:<br>
        </p>
<pre class="programlisting"><span class="identifier">co_spawn</span><span class="special">(</span><span class="identifier">executor</span><span class="special">,</span>
    <span class="special">[</span><span class="identifier">socket</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">socket</span><span class="special">)]()</span> <span class="keyword">mutable</span>
    <span class="special">{</span>
      <span class="keyword">return</span> <span class="identifier">echo</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">socket</span><span class="special">));</span>
    <span class="special">},</span>
    <span class="identifier">detached</span><span class="special">);</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Added a new constructor overload to <code class="computeroutput"><span class="identifier">use_awaitable_t</span></code>'s
          default executor adapter, to enable conversion between executor types.
        </li>
<li class="listitem">
          Added support for using <code class="computeroutput"><span class="identifier">detached_t</span></code>
          as a default completion token, by adding members <code class="computeroutput"><span class="identifier">as_default_on</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">as_default_on_t</span><span class="special">&lt;&gt;</span></code>.
        </li>
<li class="listitem">
          Added a move constructor to <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code>.
        </li>
<li class="listitem">
          Changed <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code>
          write operations to linearise gather-write buffer sequences.
        </li>
<li class="listitem">
          Added compile-time detection of the deprecated <code class="computeroutput"><span class="identifier">asio_handler_invoke</span></code>
          hook. This hook was deprecated with the introduction of the Networking
          TS trait <code class="computeroutput"><span class="identifier">associated_executor</span></code>
          and function <code class="computeroutput"><span class="identifier">get_associated_executor</span><span class="special">()</span></code>. Compiling an application with <code class="computeroutput"><span class="identifier">BOOST_ASIO_NO_DEPRECATED</span></code> will now trigger
          a compile error if any handler implements the <code class="computeroutput"><span class="identifier">asio_handler_invoke</span></code>
          hook.
        </li>
<li class="listitem">
          Added compile-time detection of the deprecated <code class="computeroutput"><span class="identifier">asio_handler_allocate</span></code>
          and <code class="computeroutput"><span class="identifier">asio_handle_deallocate</span></code>
          hooks. These hooks were deprecated with the introduction of the Networking
          TS trait <code class="computeroutput"><span class="identifier">associated_allocator</span></code>
          and function <code class="computeroutput"><span class="identifier">get_associated_allocator</span><span class="special">()</span></code>. Compiling an application with <code class="computeroutput"><span class="identifier">BOOST_ASIO_NO_DEPRECATED</span></code> will now trigger
          a compile error if any handler implements the <code class="computeroutput"><span class="identifier">asio_handler_allocate</span></code>
          or <code class="computeroutput"><span class="identifier">asio_handler_deallocate</span></code>
          hooks.
        </li>
<li class="listitem">
          Implemented a number of performance optimisations, including:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Specialising single-buffer operations to use <code class="computeroutput"><span class="identifier">recv</span></code>
                rather than <code class="computeroutput"><span class="identifier">recvmsg</span></code>,
                <code class="computeroutput"><span class="identifier">send</span></code> rather than
                <code class="computeroutput"><span class="identifier">sendmsg</span></code>, <code class="computeroutput"><span class="identifier">read</span></code> rather than <code class="computeroutput"><span class="identifier">readv</span></code>, and <code class="computeroutput"><span class="identifier">write</span></code>
                rather than <code class="computeroutput"><span class="identifier">writev</span></code>.
              </li>
<li class="listitem">
                Lightening the reference counting overhead of the polymorphic wrapper
                <code class="computeroutput"><span class="identifier">executor</span></code>.
              </li>
<li class="listitem">
                Returning from system call operation wrappers as early as possible,
                and only accessing <code class="computeroutput"><span class="identifier">errno</span></code>
                and error codes when on an error path.
              </li>
<li class="listitem">
                Applying additional optimisations if a "native" I/O executor
                (such as <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">exeutor_type</span></code>)
                is detected.
              </li>
</ul></div>
        </li>
<li class="listitem">
<p class="simpara">
          Added source location support to handler tracking. The new <code class="computeroutput"><span class="identifier">BOOST_ASIO_HANDLER_LOCATION</span><span class="special">((</span><span class="identifier">file_name</span><span class="special">,</span>
          <span class="identifier">line</span><span class="special">,</span>
          <span class="identifier">function_name</span><span class="special">))</span></code>
          macro may be used to inform the handler tracking mechanism of a source
          location. This macro declares an object that is placed on the stack. Then,
          when an asynchronous operation is launched with location information, it
          outputs lines using the <span class="bold"><strong>&lt;action&gt;</strong></span>
          <code class="literal">n^m</code>, prior to the <code class="literal">n*m</code> line that signifies
          the beginning of the asynchronous operation. For example:
        </p>
<pre class="programlisting">  @asio|1589423304.861944|&gt;7|ec=system:0,bytes_transferred=5
  @asio|1589423304.861952|7^8|in 'async_write' (.<span class="emphasis"><em>..</em></span>../../include/asio/impl/write.hpp:330)
  @asio|1589423304.861952|7^8|called from 'do_write' (handler_tracking/async_tcp_echo_server.cpp:62)
  @asio|1589423304.861952|7^8|called from 'operator()' (handler_tracking/async_tcp_echo_server.cpp:51)
  @asio|1589423304.861952|7*8|socket@0x7ff61c008230.async_send
  @asio|1589423304.861975|.8|non_blocking_send,ec=system:0,bytes_transferred=5
  @asio|1589423304.861980|&lt;7|</pre>
<p class="simpara">
          <br> If <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">source_location</span></code> or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">source_location</span></code>
          are available, the <code class="computeroutput"><span class="identifier">use_awaitable_t</span></code>
          token (when default-constructed or used as a default completion token)
          will also cause handler tracking to output a source location for each newly
          created asynchronous operation. A <code class="computeroutput"><span class="identifier">use_awaitable_t</span></code>
          object may also be explicitly constructed with location information.
        </p>
</li>
<li class="listitem">
          Implemented various improvements to the <code class="literal">handlerviz.pl</code>
          tool.
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Add nodes for pending handlers at bottom of graph, outlined in red.
              </li>
<li class="listitem">
                Display source location in a tooltip on the edge label (for SVG).
              </li>
<li class="listitem">
                Use invisible nodes to enforce order to keep related control flow
                vertical.
              </li>
</ul></div>
        </li>
<li class="listitem">
<p class="simpara">
          Added the <code class="literal">handlerlive.pl</code> tool, which processes handler
          tracking output to produce a list of "live" handlers. Live handlers
          are those that are associated with pending asynchronous operations, as
          well as handlers that are currently executing. For example:
        </p>
<pre class="programlisting"><span class="identifier">cat</span> <span class="identifier">output</span><span class="special">.</span><span class="identifier">txt</span> <span class="special">|</span> <span class="identifier">perl</span> <span class="identifier">handlerlive</span><span class="special">.</span><span class="identifier">pl</span>
</pre>
<p class="simpara">
          or:
        </p>
<pre class="programlisting"><span class="identifier">perl</span> <span class="identifier">handerlive</span><span class="special">.</span><span class="identifier">pl</span> <span class="special">&lt;</span> <span class="identifier">output</span><span class="special">.</span><span class="identifier">txt</span>
</pre>
<p class="simpara">
          or:
        </p>
<pre class="programlisting"><span class="identifier">perl</span> <span class="identifier">handlerlive</span><span class="special">.</span><span class="identifier">pl</span> <span class="identifier">output</span><span class="special">.</span><span class="identifier">txt</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Added the <code class="literal">handlertree.pl</code> tool, which filters handler
          tracking output to include only those events in the tree that produced
          the nominated handlers. For example, to filter the output to include only
          the events associated with handlers <code class="computeroutput"><span class="number">123</span></code>,
          <code class="computeroutput"><span class="number">456</span></code>, and their predecessors:
        </p>
<pre class="programlisting">  cat output.txt | perl handlertree.pl 123 456</pre>
<p class="simpara">
          or:
        </p>
<pre class="programlisting">  perl handlertree.pl 123 456 &lt; output.txt</pre>
<p class="simpara">
          <br> This script may be combined with handerlive.pl and handlerviz.pl
          to produce a graph of the "live" asynchronous operation chains.
          For example:
        </p>
<pre class="programlisting">  cat output.txt | \
    perl handlertree.pl <code class="computeroutput"><span class="identifier">perl</span> <span class="identifier">handlerlive</span><span class="special">.</span><span class="identifier">pl</span> <span class="identifier">output</span><span class="special">.</span><span class="identifier">txt</span></code> | \
    perl handlerviz.pl | \
    dot -Tsvg &gt; output.svg</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Added changes for clang-based Embarcadero C++ compilers.
        </li>
<li class="listitem">
          Fixed a deadlock that can occur when multiple threads concurrently initialise
          the Windows I/O completion port backend.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">async_compose</span></code> to
          work with copyable handlers when passed by lvalue.
        </li>
<li class="listitem">
          Fixed completion signature deduction in <code class="computeroutput"><span class="identifier">co_spawn</span></code>.
        </li>
<li class="listitem">
          Removed a spurious <code class="computeroutput"><span class="identifier">Executor</span></code>
          base class from the <code class="computeroutput"><span class="identifier">executor_binder</span></code>
          implementation.
        </li>
<li class="listitem">
          Various fixes and improvements in the documentation and examples.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h26"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_16_1___boost_1_73"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_16_1___boost_1_73">Asio
      1.16.1 / Boost 1.73</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed compatibility with C++20 concept syntax.
        </li>
<li class="listitem">
          Marked the POSIX descriptor classes' move constructors as <code class="computeroutput"><span class="keyword">noexcept</span></code>.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">host_name_verification</span></code> class, which is
          a drop-in replacement for <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">rfc2818_verification</span></code>.
          The <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">rfc2818_verification</span></code> class has been marked
          as deprecated. As a consequence of this change, SSL support now depends
          on functions that were introduced in OpenSSL 1.0.2.
        </li>
<li class="listitem">
          Added an <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span></code> constructor to take ownership
          of a native handle.
        </li>
<li class="listitem">
          Changed C++ language version detection with <code class="literal">gcc</code> to use
          <code class="computeroutput"><span class="identifier">__cplusplus</span></code> macro.
        </li>
<li class="listitem">
          Fixed a work counting issue in the asynchronous resolve operation for endpoints.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">strand</span><span class="special">&lt;&gt;</span></code>
          converting constructors and assignment operators.
        </li>
<li class="listitem">
          Ensured that resolvers are restarted correctly after a fork.
        </li>
<li class="listitem">
          Fixed compatibility with the current NetBSD release.
        </li>
<li class="listitem">
          Removed spurious handler requirement checks in some <code class="computeroutput"><span class="identifier">async_read</span></code>
          overloads.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span></code> class to propagate non-EOF errors
          from the <code class="computeroutput"><span class="identifier">add_certificate_authority</span></code>
          function.
        </li>
<li class="listitem">
          Fixed a Windows-specific <code class="computeroutput"><span class="identifier">thread_pool</span></code>
          destructor hang that occurred when the pool had an associated I/O object.
        </li>
<li class="listitem">
          Changed the <code class="literal">select</code> reactor to recreate the "self
          pipe trick" sockets on error. This addresses an issue on some versions
          of Windows, where these sockets are discconected after a system sleep.
        </li>
<li class="listitem">
          Fixed a compile error in the buffered streams due to the lack of reference
          collapsing in C++98.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">priority_scheduler</span></code>
          example to demonstrate calls to <code class="computeroutput"><span class="identifier">shutdown</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">destroy</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Removed some unnecessary null pointer checks.
        </li>
<li class="listitem">
          Changed Windows platform detection to recognise TV titles as Windows apps.
        </li>
<li class="listitem">
          Added some emscripten compatibility patches.
        </li>
<li class="listitem">
          Fixed a compile error in the <code class="computeroutput"><span class="identifier">use_awaitable_t</span><span class="special">::</span><span class="identifier">as_default_on</span></code>
          function.
        </li>
<li class="listitem">
          Changed all uses of the boost.bind placeholders to use the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">placeholders</span></code> namespace.
        </li>
<li class="listitem">
          Fixed a potential compile error in the <code class="computeroutput"><span class="identifier">async_compose</span></code>
          implementation due to incorrect overload selection.
        </li>
<li class="listitem">
          Suppressed some non-virtual destructor warnings.
        </li>
<li class="listitem">
          Various documentation fixes and improvements.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h27"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_16_0___boost_1_72"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_16_0___boost_1_72">Asio
      1.16.0 / Boost 1.72</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">async_initiate</span></code>
          helper function to automatically deduce its return type. This is enabled
          for C++11 or later.
        </li>
<li class="listitem">
          Changed all asynchronous operations to use automatically deduced return
          types. This allows completion token implementations to incorporate the
          asynchronous operation initiation into the initiating function's return
          type, without type erasure. Note that C++14 or later is required to support
          completion tokens that use per-operation return type deduction. For C++11
          or earlier, a completion token's async_result specialisation must still
          provide the nested typedef <code class="computeroutput"><span class="identifier">return_type</span></code>.
        </li>
<li class="listitem">
          Introduced three new concepts to support <code class="computeroutput"><span class="identifier">async_initiate</span></code>.
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                <code class="computeroutput"><span class="identifier">completion_signature</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;</span></code>: Checks if <code class="computeroutput"><span class="identifier">T</span></code>
                is a signature of the form <code class="computeroutput"><span class="identifier">R</span><span class="special">(</span><span class="identifier">Args</span><span class="special">...)</span></code>.
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">completion_handler_for</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">Signature</span><span class="special">&gt;</span></code>: Checks if <code class="computeroutput"><span class="identifier">T</span></code>
                is usable as a completion handler with the specified signature.
              </li>
<li class="listitem">
                <code class="computeroutput"><span class="identifier">completion_token_for</span><span class="special">&lt;</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">Signature</span><span class="special">&gt;</span></code>: Checks if <code class="computeroutput"><span class="identifier">T</span></code>
                is a completion token that can be used with async_initiate and the
                specified signature.
              </li>
<li class="listitem">
                For backward compatibility with pre-concepts C++, the macros <code class="computeroutput"><span class="identifier">BOOST_ASIO_COMPLETION_SIGNATURE</span></code>,
                <code class="computeroutput"><span class="identifier">BOOST_ASIO_COMPLETION_HANDLER_FOR</span></code>,
                and <code class="computeroutput"><span class="identifier">BOOST_ASIO_COMPLETION_TOKEN_FOR</span></code>
                are provided. These macros expand to <code class="computeroutput"><span class="keyword">typename</span></code>
                when concepts are unsupported.
              </li>
</ul></div>
        </li>
<li class="listitem">
<p class="simpara">
          Added the nested template type <code class="computeroutput"><span class="identifier">rebind_executor</span></code>
          to all I/O object types, as a way to generically rebind them to use alternative
          I/O executors. For example:
        </p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">my_socket_type</span> <span class="special">=</span> <span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">::</span><span class="identifier">rebind_executor</span><span class="special">&lt;</span><span class="identifier">my_executor_type</span><span class="special">&gt;::</span><span class="identifier">other</span><span class="special">;</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Changed the asynchronous operations' initiation function objects to report
          their associated I/O executor via the nested type <code class="computeroutput"><span class="identifier">executor_type</span></code>
          and member function <code class="computeroutput"><span class="identifier">get_executor</span><span class="special">()</span></code>. Note that the presence of <code class="computeroutput"><span class="identifier">executor_type</span></code> and <code class="computeroutput"><span class="identifier">get_executor</span><span class="special">()</span></code> should be treated as optional, and consequently
          it may be preferable to access them via the <code class="computeroutput"><span class="identifier">associated_executor</span></code>
          trait and the <code class="computeroutput"><span class="identifier">get_associated_executor</span><span class="special">()</span></code> helper function.
        </li>
<li class="listitem">
<p class="simpara">
          Added the <code class="computeroutput"><span class="identifier">default_completion_token</span></code>
          trait, so that every I/O executor type now has an associated default completion
          token type. This trait may be used in asynchronous operation declarations
          as follows:
        </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span>
    <span class="keyword">typename</span> <span class="identifier">IoObject</span><span class="special">,</span>
    <span class="keyword">typename</span> <span class="identifier">CompletionToken</span> <span class="special">=</span>
      <span class="keyword">typename</span> <span class="identifier">default_completion_token</span><span class="special">&lt;</span>
        <span class="keyword">typename</span> <span class="identifier">IoObject</span><span class="special">::</span><span class="identifier">executor_type</span>
      <span class="special">&gt;::</span><span class="identifier">type</span>
  <span class="special">&gt;</span>
<span class="keyword">auto</span> <span class="identifier">async_fyz</span><span class="special">(</span>
    <span class="identifier">IoObject</span><span class="special">&amp;</span> <span class="identifier">io_object</span><span class="special">,</span>
    <span class="identifier">CompletionToken</span><span class="special">&amp;&amp;</span> <span class="identifier">token</span> <span class="special">=</span>
      <span class="keyword">typename</span> <span class="identifier">default_completion_token</span><span class="special">&lt;</span>
        <span class="keyword">typename</span> <span class="identifier">IoObject</span><span class="special">::</span><span class="identifier">executor_type</span>
      <span class="special">&gt;::</span><span class="identifier">type</span><span class="special">{}</span>
  <span class="special">);</span>
</pre>
<p class="simpara">
          <br> If not specialised, this trait type is <code class="computeroutput"><span class="keyword">void</span></code>,
          meaning no default completion token type is available for the given I/O
          executor.
        </p>
</li>
<li class="listitem">
<p class="simpara">
          Specialised the <code class="computeroutput"><span class="identifier">default_completion_token</span></code>
          trait for the <code class="computeroutput"><span class="identifier">use_awaitable</span></code>
          completion token, so that it may be used as shown in the following example:
        </p>
<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">socket</span> <span class="special">=</span> <span class="identifier">use_awaitable</span><span class="special">.</span><span class="identifier">as_default_on</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">(</span><span class="identifier">my_context</span><span class="special">));</span>
<span class="comment">// ...</span>
<span class="identifier">co_await</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">async_connect</span><span class="special">(</span><span class="identifier">my_endpoint</span><span class="special">);</span> <span class="comment">// Defaults to use_awaitable.</span>
</pre>
<p class="simpara">
          <br> In this example, the type of the <code class="computeroutput"><span class="identifier">socket</span></code>
          object is transformed from <code class="computeroutput"><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span></code>
          to have an I/O executor with the default completion token set to <code class="computeroutput"><span class="identifier">use_awaitable</span></code>. Alternatively, the socket
          type may be computed directly:
        </p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">tcp_socket</span> <span class="special">=</span> <span class="identifier">use_awaitable_t</span><span class="special">&lt;&gt;::</span><span class="identifier">as_default_on_t</span><span class="special">&lt;</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&gt;;</span>
<span class="identifier">tcp_socket</span> <span class="identifier">socket</span><span class="special">(</span><span class="identifier">my_context</span><span class="special">);</span>
<span class="comment">// ...</span>
<span class="identifier">co_await</span> <span class="identifier">socket</span><span class="special">.</span><span class="identifier">async_connect</span><span class="special">(</span><span class="identifier">my_endpoint</span><span class="special">);</span> <span class="comment">// Defaults to use_awaitable.</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Added missing <code class="computeroutput"><span class="identifier">async_initiate</span></code>
          to the Windows-specific I/O objects' asynchronous operations.
        </li>
<li class="listitem">
<p class="simpara">
          Ensured that the executor type is propagated to newly accepted sockets.
          When synchronously or asynchronously accepting a new connection, but without
          specifying an executor or execution context, the accept operation will
          now correctly propagate the executor type from the acceptor to the socket.
          For example, if your acceptor type is:
        </p>
<pre class="programlisting"><span class="identifier">basic_socket_acceptor</span><span class="special">&lt;</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">,</span> <span class="identifier">my_executor_type</span><span class="special">&gt;</span>
</pre>
<p class="simpara">
          <br> then your accepted socket type will be:
        </p>
<pre class="programlisting"><span class="identifier">basic_stream_socket</span><span class="special">&lt;</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">,</span> <span class="identifier">my_executor_type</span><span class="special">&gt;</span>
</pre>
<p class="simpara">
          <br>
        </p>
</li>
<li class="listitem">
          Changed to require that <code class="computeroutput"><span class="identifier">Protocol</span></code>
          copy and move operations never throw.
        </li>
<li class="listitem">
          Changed to require that <code class="computeroutput"><span class="identifier">Endpoint</span></code>
          default constructor and move operations never throw.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="keyword">noexcept</span></code> qualifier
          to protocol accessors.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="keyword">noexcept</span></code> qualifier
          to socket move constructors.
        </li>
<li class="listitem">
          Fixed issues associated with opening serial ports on Windows:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Use the correct constant to initialise the RTS control flag.
              </li>
<li class="listitem">
                Specify a default baud rate (9600).
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a lost "outstanding work count" that can occur when an
          asynchronous accept operation is automatically restarted.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h28"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_14_1___boost_1_71"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_14_1___boost_1_71">Asio
      1.14.1 / Boost 1.71</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Improved performance slightly by eliminating a redundant move construction
          when completed handlers are dispatched.
        </li>
<li class="listitem">
          Eliminated a compiler warning by annotating a <code class="computeroutput"><span class="keyword">case</span></code>
          fall-through in the free function <code class="computeroutput"><span class="identifier">connect</span><span class="special">()</span></code> implementation.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">is_</span><span class="special">*</span><span class="identifier">_buffer_sequence</span></code> detection traits for
          user-defined sequence types.
        </li>
<li class="listitem">
          Fixed some Windows-specific warnings about an incompatible pointer cast
          when obtaining the <code class="computeroutput"><span class="identifier">CancelIoEx</span></code>
          entry point.
        </li>
<li class="listitem">
          Changed to automatically set the defaults when opening a serial port on
          Windows.
        </li>
<li class="listitem">
          Changed the serial port <code class="computeroutput"><span class="identifier">get_option</span><span class="special">()</span></code> member function to be const.
        </li>
<li class="listitem">
          Fixed a name hiding issue with the WinRT stream-oriented socket backend's
          <code class="computeroutput"><span class="identifier">shutdown</span></code> function.
        </li>
<li class="listitem">
          Applied a minor fix to the documentation for <code class="computeroutput"><span class="identifier">is_dynamic_buffer</span></code>.
        </li>
<li class="listitem">
          Added some support for Haiku OS.
        </li>
<li class="listitem">
          Added wolfSSL compatability.
        </li>
<li class="listitem">
          Changed to require C++17 or later for coroutines TS support with clang.
        </li>
<li class="listitem">
          Fixed a doxygen generation problem in the tutorial.
        </li>
<li class="listitem">
          Ensured example programs are correctly incorporated into the documentation.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h29"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_14_0___boost_1_70"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_14_0___boost_1_70">Asio
      1.14.0 / Boost 1.70</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added custom I/O executor support to I/O objects.
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                All I/O objects now have an additional <code class="computeroutput"><span class="identifier">Executor</span></code>
                template parameter. This template parameter defaults to the <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">executor</span></code> type (the polymorphic
                executor wrapper) but can be used to specify a user-defined executor
                type.
              </li>
<li class="listitem">
                I/O objects' constructors and functions that previously took an
                <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">&amp;</span></code>
                now accept either an <code class="computeroutput"><span class="identifier">Executor</span></code>
                or a reference to a concrete <code class="computeroutput"><span class="identifier">ExecutionContext</span></code>
                (such as <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span></code> or <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">thread_pool</span></code>).
              </li>
<li class="listitem">
<p class="simpara">
                Note: One potential source of breakage in existing user code is when
                reusing an I/O object's <code class="computeroutput"><span class="identifier">io_context</span></code>
                for constructing another I/O object, as in:
              </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">my_timer</span><span class="special">(</span><span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">get_executor</span><span class="special">().</span><span class="identifier">context</span><span class="special">());</span>
</pre>
<p class="simpara">
                <br> To fix this, either construct the second I/O object using
                the first I/O object's executor:<br>
              </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">my_timer</span><span class="special">(</span><span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">get_executor</span><span class="special">());</span>
</pre>
<p class="simpara">
                <br> or otherwise explicitly pass the <code class="computeroutput"><span class="identifier">io_context</span></code>:<br>
              </p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">my_timer</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>
</pre>
<p class="simpara">
                <br>
              </p>
</li>
<li class="listitem">
                The previously deprecated <code class="computeroutput"><span class="identifier">get_io_context</span></code>
                and <code class="computeroutput"><span class="identifier">get_io_service</span></code>
                member functions have now been removed.
              </li>
<li class="listitem">
                The previously deprecated service template parameters, and the corresponding
                classes, have now been removed.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">async_result</span></code>
          form with an <code class="computeroutput"><span class="identifier">initiate</span></code> static
          member function.
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p class="simpara">
                The <code class="computeroutput"><span class="identifier">async_result</span></code>
                template now supports a new form:
              </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">CompletionToken</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Signature</span><span class="special">&gt;</span>
<span class="keyword">struct</span> <span class="identifier">async_result</span>
<span class="special">{</span>
  <span class="keyword">typedef</span> <span class="comment">/* ... */</span> <span class="identifier">return_type</span><span class="special">;</span>

  <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Initiation</span><span class="special">,</span>
      <span class="keyword">typename</span> <span class="identifier">RawCompletionToken</span><span class="special">,</span>
      <span class="keyword">typename</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">&gt;</span>
  <span class="keyword">static</span> <span class="identifier">return_type</span> <span class="identifier">initiate</span><span class="special">(</span>
      <span class="identifier">Initiation</span><span class="special">&amp;&amp;</span> <span class="identifier">initiation</span><span class="special">,</span>
      <span class="identifier">RawCompletionToken</span><span class="special">&amp;&amp;</span> <span class="identifier">token</span><span class="special">,</span>
      <span class="identifier">Args</span><span class="special">&amp;&amp;...</span> <span class="identifier">args</span><span class="special">);</span>
<span class="special">};</span>
</pre>
<p class="simpara">
                <br>
              </p>
</li>
<li class="listitem">
                The <code class="computeroutput"><span class="identifier">initiate</span></code> member
                function must: (a) transform the token into a completion handler
                object <code class="computeroutput"><span class="identifier">handler</span></code>; (b)
                cause the invocation of the function object <code class="computeroutput"><span class="identifier">initiation</span></code>
                as if by calling <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span><span class="identifier">Initiation</span><span class="special">&gt;(</span><span class="identifier">initiation</span><span class="special">)(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">handler</span><span class="special">),</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special">&lt;</span><span class="identifier">Args</span><span class="special">&gt;(</span><span class="identifier">args</span><span class="special">)...)</span></code>. Note that the invocation of
                <code class="computeroutput"><span class="identifier">initiation</span></code> may be
                deferred (e.g. lazily evaluated), in which case <code class="computeroutput"><span class="identifier">initiation</span></code>
                and <code class="computeroutput"><span class="identifier">args</span></code> must be
                decay-copied and moved as required.
              </li>
<li class="listitem">
                A helper function template <code class="computeroutput"><span class="identifier">async_initiate</span></code>
                has also been added as a wrapper for the invocation of <code class="computeroutput"><span class="identifier">async_result</span><span class="special">&lt;&gt;::</span><span class="identifier">initiate</span></code>. For backward compatibility,
                this function supports both the old and new <code class="computeroutput"><span class="identifier">async_result</span></code>
                forms.
              </li>
<li class="listitem">
                The composed operations examples have been updated to use <code class="computeroutput"><span class="identifier">async_initiate</span></code>.
              </li>
<li class="listitem">
                The previously deprecated <code class="computeroutput"><span class="identifier">handler_type</span></code>
                trait and single-argument form of <code class="computeroutput"><span class="identifier">async_result</span></code>
                have now been removed.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Updated the Coroutines TS support and promoted it to the <code class="computeroutput"><span class="identifier">asio</span></code> namespace.
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                The <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>,
                <code class="computeroutput"><span class="identifier">co_spawn</span></code>, <code class="computeroutput"><span class="identifier">this_coro</span></code>, <code class="computeroutput"><span class="identifier">detached</span></code>,
                and <code class="computeroutput"><span class="identifier">redirect_error</span></code>
                facilities have been moved from the <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">experimental</span></code>
                namespace to namespace <code class="computeroutput"><span class="identifier">asio</span></code>.
                As part of this change, the <code class="computeroutput"><span class="identifier">this_coro</span><span class="special">::</span><span class="identifier">token</span><span class="special">()</span></code> awaitable has been superseded by
                the <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_awaitable</span></code> completion token.
              </li>
<li class="listitem">
                Please note that the <code class="computeroutput"><span class="identifier">use_awaitable</span></code>
                and <code class="computeroutput"><span class="identifier">redirect_error</span></code>
                completion tokens work only with asynchronous operations that use
                the new form of <code class="computeroutput"><span class="identifier">async_result</span></code>
                with member function <code class="computeroutput"><span class="identifier">initiate</span></code>.
                Furthermore, when using <code class="computeroutput"><span class="identifier">use_awaitable</span></code>,
                please be aware that the asynchronous operation is not initiated
                until <code class="computeroutput"><span class="identifier">co_await</span></code> is
                applied to the <code class="computeroutput"><span class="identifier">awaitable</span><span class="special">&lt;&gt;</span></code>.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">DynamicBuffer_v2</span></code>
          concept which is CopyConstructible.
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<p class="simpara">
                This change adds a new set of type requirements for dynamic buffers,
                <code class="computeroutput"><span class="identifier">DynamicBuffer_v2</span></code>,
                which supports copy construction. These new type requirements enable
                dynamic buffers to be used as arguments to user-defined composed
                operations, where the same dynamic buffer object is used repeatedly
                for multiple underlying operations. For example:<br>
              </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">DynamicBuffer</span><span class="special">&gt;</span>
<span class="keyword">void</span> <span class="identifier">echo_line</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;</span> <span class="identifier">sock</span><span class="special">,</span> <span class="identifier">DynamicBuffer</span> <span class="identifier">buf</span><span class="special">)</span>
<span class="special">{</span>
  <span class="identifier">n</span> <span class="special">=</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">read_until</span><span class="special">(</span><span class="identifier">sock</span><span class="special">,</span> <span class="identifier">buf</span><span class="special">,</span> <span class="char">'\n'</span><span class="special">);</span>
  <span class="identifier">asio</span><span class="special">::</span><span class="identifier">write</span><span class="special">(</span><span class="identifier">sock</span><span class="special">,</span> <span class="identifier">buf</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">transfer_exactly</span><span class="special">(</span><span class="identifier">n</span><span class="special">));</span>
<span class="special">}</span>
</pre>
<p class="simpara">
                <br>
              </p>
</li>
<li class="listitem">
                The original <code class="computeroutput"><span class="identifier">DynamicBuffer</span></code>
                type requirements have been renamed to <code class="computeroutput"><span class="identifier">DynamicBuffer_v1</span></code>.
                These requirements continue to be compatible with the Networking
                TS.
              </li>
<li class="listitem">
                New type traits <code class="computeroutput"><span class="identifier">is_dynamic_buffer_v1</span></code>
                and <code class="computeroutput"><span class="identifier">is_dynamic_buffer_v2</span></code>
                have been added to test for conformance to <code class="computeroutput"><span class="identifier">DynamicBuffer_v1</span></code>
                and <code class="computeroutput"><span class="identifier">DynamicBuffer_v2</span></code>
                respectively. The existing <code class="computeroutput"><span class="identifier">is_dynamic_buffer</span></code>
                trait has been retained and delegates to <code class="computeroutput"><span class="identifier">is_dynamic_buffer_v1</span></code>
                (unless <code class="computeroutput"><span class="identifier">BOOST_ASIO_NO_DYNAMIC_BUFFER_V1</span></code>
                is explicitly defined, in which case it delegates to <code class="computeroutput"><span class="identifier">is_dynamic_buffer_v2</span></code>).
              </li>
<li class="listitem">
                For convenience, the <code class="computeroutput"><span class="identifier">dynamic_string_buffer</span></code>
                and <code class="computeroutput"><span class="identifier">dynamic_vector_buffer</span></code>
                classes conform to both <code class="computeroutput"><span class="identifier">DynamicBuffer_v1</span></code>
                and <code class="computeroutput"><span class="identifier">DynamicBuffer_v2</span></code>
                requirements.
              </li>
<li class="listitem">
                When <code class="computeroutput"><span class="identifier">BOOST_ASIO_NO_DYNAMIC_BUFFER_V1</span></code>
                is defined, all support for <code class="computeroutput"><span class="identifier">DynamicBuffer_v1</span></code>
                types and functions is #ifdef-ed out. Support for using <code class="computeroutput"><span class="identifier">basic_streambuf</span></code> with the <code class="computeroutput"><span class="identifier">read</span></code>, <code class="computeroutput"><span class="identifier">async_read</span></code>,
                <code class="computeroutput"><span class="identifier">read_until</span></code>, <code class="computeroutput"><span class="identifier">async_read_until</span></code>, <code class="computeroutput"><span class="identifier">write</span></code>, and <code class="computeroutput"><span class="identifier">async_write</span></code>
                functions is also disabled as a consequence.
              </li>
<li class="listitem">
                Note: This change should have no impact on existing source code that
                simply uses dynamic buffers in conjunction with Asio's composed operations.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">async_compose</span></code>
          function that simplifies the implementation of user-defined asynchronous
          operations.
        </li>
<li class="listitem">
          Added a <code class="computeroutput"><span class="identifier">make_strand</span></code> function,
          which creates a <code class="computeroutput"><span class="identifier">strand</span></code>
          with a deduced <code class="computeroutput"><span class="identifier">Executor</span></code>
          template argument.
        </li>
<li class="listitem">
          Relaxed the completion condition type requirements to only require move-constructibility
          rather than copy-constructibility.
        </li>
<li class="listitem">
          Added a constructor for <code class="computeroutput"><span class="identifier">local</span><span class="special">::</span><span class="identifier">basic_endpoint</span></code>
          that takes a <code class="computeroutput"><span class="identifier">string_view</span></code>.
        </li>
<li class="listitem">
          Added the noexcept qualifier to various member functions of the <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address</span></code>, <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v4</span></code>,
          <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v6</span></code>, <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">basic_endpoint</span></code>,
          and <code class="computeroutput"><span class="identifier">executor_work_guard</span></code>
          classes.
        </li>
<li class="listitem">
          Added the noexcept qualifier to the <code class="computeroutput"><span class="identifier">buffer_sequence_begin</span></code>
          and <code class="computeroutput"><span class="identifier">buffer_sequence_end</span></code>
          functions.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_VISIBILITY</span></code>
          configuration <code class="computeroutput"><span class="preprocessor">#define</span></code>
          that allows visibility pragmas to be disabled. (Note: If symbols are hidden,
          extra care must be taken to ensure that Asio types are not passed across
          shared library API boundaries.)
        </li>
<li class="listitem">
          Enabled recycling of the memory used to type-erase a function object with
          the polymorphic executor.
        </li>
<li class="listitem">
          Changed receive operations to return the correct number of bytes transferred
          when truncation (<code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">message_size</span></code>)
          occurs on a datagram-oriented socket.
        </li>
<li class="listitem">
          Fixed multicast behaviour on QNX by automatically applying <code class="computeroutput"><span class="identifier">SO_REUSEPORT</span></code> when the <code class="computeroutput"><span class="identifier">reuse_address</span></code>
          option is set.
        </li>
<li class="listitem">
          Added inclusion of <code class="computeroutput"><span class="identifier">unistd</span><span class="special">.</span><span class="identifier">h</span></code> when
          targeting Haiku OS, to fix feature detection.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">network_v</span><span class="special">[</span><span class="number">46</span><span class="special">].</span><span class="identifier">hpp</span></code>
          headers to the top-level convenience header.
        </li>
<li class="listitem">
          Fixed calculation of absolute timeout when the backend uses <code class="computeroutput"><span class="identifier">pthread_cond_timedwait</span></code>.
        </li>
<li class="listitem">
          Changed the range-based asynchronous connect operation to deduce the <code class="computeroutput"><span class="identifier">EndpointSequence</span></code> iterator type rather
          than assume the presence of a <code class="computeroutput"><span class="identifier">const_iterator</span></code>
          typedef.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">buffer_sequence_begin</span></code>
          and <code class="computeroutput"><span class="identifier">buffer_sequence_end</span></code>
          to prevent implicit conversion. This change addresses an issue where a
          call to <code class="computeroutput"><span class="identifier">buffer_sequence_begin</span></code>
          or <code class="computeroutput"><span class="identifier">buffer_sequence_end</span></code>
          could trigger an implicit conversion to <code class="computeroutput"><span class="identifier">const_buffer</span></code>
          or <code class="computeroutput"><span class="identifier">mutable_buffer</span></code>. Whenever
          this implicit conversion occurred, the return value of <code class="computeroutput"><span class="identifier">buffer_sequence_begin</span></code>
          or <code class="computeroutput"><span class="identifier">buffer_sequence_end</span></code>
          would point to a temporary object.
        </li>
<li class="listitem">
          Ensured SSL handshake errors are propagated to the peer before the local
          operation completes.
        </li>
<li class="listitem">
          Suppressed the <code class="computeroutput"><span class="identifier">eof</span></code> error
          on SSL shutdown as it actually indicates success.
        </li>
<li class="listitem">
          Added a fallback error code for when we OpenSSL produces an <code class="computeroutput"><span class="identifier">SSL_ERROR_SYSCALL</span></code> result without an associated
          error.
        </li>
<li class="listitem">
          Changed composed asynchronous read and write operations to move, rather
          than copy, the buffer sequence objects when the composed operation implementation
          is moved.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">atomic</span><span class="special">&gt;</span></code> when targeting apple/clang/libc++ with
          recent Xcode versions, even for C++03. This fixes a warning about the deprecation
          of <code class="computeroutput"><span class="identifier">OSMemoryBarrier</span></code>.
        </li>
<li class="listitem">
          Fixed compile errors that occur when using the composed read and write
          operations with MSVC 11.0, by disabling <code class="computeroutput"><span class="keyword">decltype</span></code>
          support for that compiler.
        </li>
<li class="listitem">
          Increased the default value of <code class="computeroutput"><span class="identifier">_WIN32_WINNT</span></code>
          to <code class="computeroutput"><span class="number">0x0601</span></code> (Windows 7).
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">dispatch</span></code> documentation
          to note that it may call the supplied function object in the current thread.
        </li>
<li class="listitem">
          Updated <code class="computeroutput"><span class="identifier">post</span></code> and <code class="computeroutput"><span class="identifier">defer</span></code> documentation to clarify the the
          distinction between them.
        </li>
<li class="listitem">
          Fixed compilation errors in the read and write composed operations when
          used with MSVC 11.0.
        </li>
<li class="listitem">
          Fixed a Windows-specific issue where the execution context associated with
          <code class="computeroutput"><span class="identifier">system_executor</span></code> was not
          being correctly cleaned up on exit.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h30"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_12_2___boost_1_69"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_12_2___boost_1_69">Asio
      1.12.2 / Boost 1.69</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed a problem with the detection of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span></code>
          availability with libstdc++.
        </li>
<li class="listitem">
          Fixed compile error in regex overload of <code class="computeroutput"><span class="identifier">read_until</span></code>.
        </li>
<li class="listitem">
          Fixed a timer heap corruption issue that can occur when moving a cancelled
          timer.
        </li>
<li class="listitem">
          Fixed detection of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">string_view</span></code>
          and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string_view</span></code> with newer clang/libc++.
        </li>
<li class="listitem">
          Fixed MSVC version detection for availability of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">invoke_result</span></code>.
        </li>
<li class="listitem">
          Fixed the buffer sequence traits to test the new requirements, if <code class="computeroutput"><span class="keyword">decltype</span></code> is available.
        </li>
<li class="listitem">
          Fixed an MSVC issue when building with exceptions disabled.
        </li>
<li class="listitem">
          Added SSL context options for TLS v1.3.
        </li>
<li class="listitem">
          Added a compile-time test for TLS v1 support.
        </li>
<li class="listitem">
          Fixed the macro used to test for TLS v1.2 support.
        </li>
<li class="listitem">
          Prevented global objects from being created once per thread on Windows.
        </li>
<li class="listitem">
          Fixed a crash when using <code class="computeroutput"><span class="identifier">size</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">max_size</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">empty</span><span class="special">()</span></code> on default-constructed resolver results.
        </li>
<li class="listitem">
          Changed to move the return value in basic_resolver_results::begin() to
          avoid copying.
        </li>
<li class="listitem">
          Enabled move support for the Intel Compiler.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string_view</span></code> detection issue when using
          clang-cl.
        </li>
<li class="listitem">
          Fixed the handler tracking operation name for <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">executor_type</span><span class="special">::</span><span class="identifier">dispatch</span></code>.
        </li>
<li class="listitem">
          Fixed a buffer overflow that could occur when parsing an address string
          with a 64-bit scope id.
        </li>
<li class="listitem">
          Added examples showing how to write composed operations.
        </li>
<li class="listitem">
          Added C++11 versions of the Timeouts, Timers, SOCKS4 and SSL examples.
        </li>
<li class="listitem">
          Fixed minor issues in documentation and examples.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h31"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_12_1___boost_1_67"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_12_1___boost_1_67">Asio
      1.12.1 / Boost 1.67</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added missing const qualifier to <code class="computeroutput"><span class="identifier">basic_socket_acceptor</span><span class="special">::</span><span class="identifier">get_option</span></code>.
        </li>
<li class="listitem">
          Worked around a parsing error that occurs with some versions of gcc.
        </li>
<li class="listitem">
          Fixed broken code samples in tutorial.
        </li>
<li class="listitem">
          Added new experimental features. (Note that "experimental" features
          may be changed without notice in subsequent releases.)
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Added <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">detached</span></code>
                completion token.
              </li>
<li class="listitem">
                Added <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">redirect_error</span></code>
                completion token.
              </li>
<li class="listitem">
                Added <code class="computeroutput"><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">co_spawn</span></code>
                facility for integration with the coroutines technical specification.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Updated timeout examples to use latest features.
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Used <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span></code> rather than <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">deadline_timer</span></code>.
              </li>
<li class="listitem">
                Used <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">dynamic_buffer</span></code> rather than <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span></code>.
              </li>
<li class="listitem">
                Used timed <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">run_for</span><span class="special">()</span></code>
                function for blocking clients.
              </li>
<li class="listitem">
                Added example showing a custom completion token for blocking with
                timeouts.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed unit tests to compile when <code class="computeroutput"><span class="identifier">BOOST_ASIO_NO_DEPRECATED</span></code>
          is defined.
        </li>
<li class="listitem">
          Changed socket iostreams to use chrono by default, to fix compatibility
          with the Networking TS. Define <code class="computeroutput"><span class="identifier">BOOST_ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM</span></code>
          to enable the old Boost.Date_Time interface in <code class="computeroutput"><span class="identifier">basic_socket_streambuf</span></code>
          and <code class="computeroutput"><span class="identifier">basic_socket_iostream</span></code>.
        </li>
<li class="listitem">
          Updated examples to use chrono rather than Boost.Date_Time.
        </li>
<li class="listitem">
          Fixed an incorrect member function detector in the <code class="computeroutput"><span class="identifier">is_dynamic_buffer</span></code>
          trait.
        </li>
<li class="listitem">
          Fixed an <code class="computeroutput"><span class="identifier">async_result</span></code> incompatibility
          with deprecated <code class="computeroutput"><span class="identifier">handler_type</span></code>.
        </li>
<li class="listitem">
          Added a missing move optimisation in the SSL stream implementation.
        </li>
<li class="listitem">
          Fixed incorrect <code class="computeroutput"><span class="identifier">basic_resolver_results</span><span class="special">::</span><span class="identifier">value_type</span></code>
          typedef.
        </li>
<li class="listitem">
          Fixed a compile error with some OpenSSL versions when <code class="computeroutput"><span class="identifier">SSL_OP_NO_COMPRESSION</span></code>
          is defined.
        </li>
<li class="listitem">
          Changed <code class="computeroutput"><span class="identifier">add_certificate_authority</span></code>
          to process multiple certificates in a bundle.
        </li>
<li class="listitem">
          Eliminated deprecation warning with MSVC by using <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">invoke_result</span></code>
          rather than <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">result_of</span></code>.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string_view</span></code> for C++17 or later, and
          <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">experimental</span><span class="special">::</span><span class="identifier">string_view</span></code> for C++14. Define the preprocessor
          macro <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_STD_STRING_VIEW</span></code>
          to force the use of std::experimental::string_view (assuming it is available)
          when compiling in C++17 mode.
        </li>
<li class="listitem">
          Ensured <code class="computeroutput"><span class="identifier">DynamicBuffer</span></code> template
          arguments are decayed before using in <code class="computeroutput"><span class="identifier">enable_if</span></code>
          tests.
        </li>
<li class="listitem">
          Changed documentation to distinguish legacy completion handlers (which
          are still required to be CopyConstructible) from new MoveConstructible
          handlers.
        </li>
<li class="listitem">
          Suppressed a discarded return value warning in the buffer debugging support.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">basic_yield_context</span></code>
          to work with completion signatures containing reference parameters.
        </li>
<li class="listitem">
          Ensured that stackful coroutines launched using <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code> correctly store decayed copies of their
          function and handler arguments.
        </li>
<li class="listitem">
          Fixed some compatibility issues with Android.
        </li>
<li class="listitem">
          Added cross-compilation support to Jamfiles.
        </li>
<li class="listitem">
          Fixed some minor portability issues in examples.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h32"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_12_0___boost_1_66"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_12_0___boost_1_66">Asio
      1.12.0 / Boost 1.66</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Implemented interface changes to reflect the Networking TS (<a href="../www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4656.pdf" target="_top">N4656</a>).
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                See the <a class="link" href="net_ts.html" title="Networking TS compatibility">list</a> of new interfaces
                and, where applicable, the corresponding old interfaces that have
                been superseded.
              </li>
<li class="listitem">
                The service template parameters, and the corresponding classes, are
                disabled by default. For example, instead of <code class="computeroutput"><span class="identifier">basic_socket</span><span class="special">&lt;</span><span class="identifier">Protocol</span><span class="special">,</span> <span class="identifier">SocketService</span><span class="special">&gt;</span></code> we now have simply <code class="computeroutput"><span class="identifier">basic_socket</span><span class="special">&lt;</span><span class="identifier">Protocol</span><span class="special">&gt;</span></code>.
                The old interface can be enabled by defining the <code class="computeroutput"><span class="identifier">BOOST_ASIO_ENABLE_OLD_SERVICES</span></code>
                macro.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Removed previously deprecated functions.
        </li>
<li class="listitem">
          Added support for customised handler tracking.
        </li>
<li class="listitem">
          Added reactor-related (i.e. descriptor readiness) events to handler tracking.
        </li>
<li class="listitem">
          Added special <a class="link" href="../">concurrency
          hint</a> values that may be used to disable locking on a per <code class="computeroutput"><span class="identifier">io_context</span></code> basis.
        </li>
<li class="listitem">
          Enabled perfect forwarding for the first <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code> constructor argument.
        </li>
<li class="listitem">
          Added ability to release ownership of the underlying native socket. (Requires
          Windows 8.1 or later when using the I/O completion port backend.)
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h33"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_10___boost_1_65"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_10___boost_1_65">Asio
      1.10.10 / Boost 1.65</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Changed to require <code class="literal">g++</code> versions &gt;= 4.7 to use standard
          atomics, to fix a linker error when using <code class="literal">g++</code> 4.6 (<a href="https://svn.boost.org/trac/boost/ticket/13121" target="_top">#13121</a>).
        </li>
<li class="listitem">
          Enabled use of <code class="computeroutput"><span class="keyword">constexpr</span></code> and
          variadic templates with recent MSVC versions.
        </li>
<li class="listitem">
          Fixed a race condition in the Linux epoll backend, which may occur when
          a socket or descriptor is closed while another thread is blocked on epoll.
        </li>
<li class="listitem">
          Eliminated use of deprecated <code class="computeroutput"><span class="identifier">auto_ptr</span></code>.
        </li>
<li class="listitem">
          Fixed misplaced use of <code class="computeroutput"><span class="identifier">asio_handler_is_continuation</span></code>
          result in reactive <code class="computeroutput"><span class="identifier">async_accept</span></code>
          implementation.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="identifier">poll</span><span class="special">.</span><span class="identifier">h</span></code> rather than <code class="computeroutput"><span class="identifier">sys</span><span class="special">/</span><span class="identifier">poll</span><span class="special">.</span><span class="identifier">h</span></code> on
          some modern POSIX platforms (<a href="https://svn.boost.org/trac/boost/ticket/12419" target="_top">#12419</a>).
        </li>
<li class="listitem">
          Fixed MSVC intellisense detection.
        </li>
<li class="listitem">
          Disabled use of the <code class="computeroutput"><span class="identifier">__thread</span></code>
          keyword extension for android/clang/x86 targets.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h34"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_9___boost_1_64"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_9___boost_1_64">Asio
      1.10.9 / Boost 1.64</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added limited support for using regular file descriptors (where I/O operations
          should never fail with <code class="computeroutput"><span class="identifier">EAGAIN</span></code>
          or <code class="computeroutput"><span class="identifier">EWOULDBLOCK</span></code>) with <code class="computeroutput"><span class="identifier">posix</span><span class="special">::</span><span class="identifier">stream_descriptor</span></code>, when using the Linux
          epoll backend.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="identifier">allocator_traits</span></code>
          to rebind allocators in C++11 or later.
        </li>
<li class="listitem">
          Eliminated a double "construction" issue in the converting move
          constructors.
        </li>
<li class="listitem">
          Added new <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context_base</span></code> enumerations to enable support
          for any TLS version, and improved consistency of SSL/TLS version handling
          across OpenSSL releases.
        </li>
<li class="listitem">
          Applied more changes to address OpenSSL 1.1 compatibility.
        </li>
<li class="listitem">
          Fixed a compile error when OpenSSL compression is disabled at compile time.
        </li>
<li class="listitem">
          Suppressed some spurious unused variable warnings issued by <code class="literal">gcc</code>
          (<a href="https://svn.boost.org/trac/boost/ticket/12302" target="_top">#12302</a>).
        </li>
<li class="listitem">
          Worked around a new clang warning issued for usage of the comma operator.
        </li>
<li class="listitem">
          Fixed various header ordering problems.
        </li>
<li class="listitem">
          Changed to refer <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">atomic_thread_fence</span></code>, when available,
          to eliminate a deprecated function warning on newest macOS SDK (<a href="https://svn.boost.org/trac/boost/ticket/12482" target="_top">#12482</a>).
        </li>
<li class="listitem">
          Added a workaround for broken <code class="computeroutput"><span class="identifier">getaddrinfo</span></code>
          in Apple's NAT64 environment.
        </li>
<li class="listitem">
          Fixed an exception safety issue in the internal hash map implementation.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h35"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_8___boost_1_62"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_8___boost_1_62">Asio
      1.10.8 / Boost 1.62</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added compatibility with OpenSSL 1.1.0 (<a href="https://svn.boost.org/trac/boost/ticket/12238" target="_top">#12238</a>).
        </li>
<li class="listitem">
          Fixed out-of-bounds iterator use in <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">connect</span><span class="special">()</span></code> when the <code class="computeroutput"><span class="identifier">connect_condition</span></code>
          returns an end iterator (<a href="https://svn.boost.org/trac/boost/ticket/12354" target="_top">#12354</a>).
        </li>
<li class="listitem">
          Added a workaround for a move detection problem on MSVC 2015 Update 2 (<a href="https://svn.boost.org/trac/boost/ticket/12115" target="_top">#12115</a>).
        </li>
<li class="listitem">
          Changed a workaround that was previously added for broken Windows firewalls
          to only bind to 127.0.0.1 if <code class="computeroutput"><span class="identifier">getsockname</span></code>
          reports 0.0.0.0 (<a href="https://svn.boost.org/trac/boost/ticket/12406" target="_top">#12406</a>).
        </li>
<li class="listitem">
          Added call to <code class="computeroutput"><span class="identifier">SSL_COMP_free_compression_methods</span></code>
          to fix two memory leaks reported at shutdown, for OpenSSL versions &gt;=
          1.0.2 and &lt; 1.1.0 (<a href="https://svn.boost.org/trac/boost/ticket/10795" target="_top">#10795</a>).
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">use_future</span></code> compile
          error encountered on some standard library implementations, by changing
          <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">allocator</span><span class="special">&lt;</span><span class="keyword">void</span><span class="special">&gt;</span></code>
          use to a non-void template parameter.
        </li>
<li class="listitem">
          Enabled use of native <code class="computeroutput"><span class="identifier">getaddrinfo</span></code>
          by default on Apple OSes, rather than emulation in terms of <code class="computeroutput"><span class="identifier">getipnodebyname</span></code>.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h36"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_7___boost_1_60"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_7___boost_1_60">Asio
      1.10.7 / Boost 1.60</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added support for Windows 8.1 Store apps.
        </li>
<li class="listitem">
          Fixed macro multiple definition error on Microsoft Visual Studio 2015 (<a href="https://svn.boost.org/trac/boost/ticket/11539" target="_top">#11539</a>).
        </li>
<li class="listitem">
          Changed Asio's SSL wrapper to respect OpenSSL's <code class="computeroutput"><span class="identifier">OPENSSL_NO_SSL3</span></code>
          feature test <code class="computeroutput"><span class="preprocessor">#define</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/11754" target="_top">#11754</a>).
        </li>
<li class="listitem">
          Changed Asio's SSL wrapper to use OpenSSL's new <code class="computeroutput"><span class="identifier">SSL_CTX_clear_chain_certs</span></code>
          function, if available.
        </li>
<li class="listitem">
          Suppressed a clang 3.6+ warning about unused typedefs (<a href="https://svn.boost.org/trac/boost/ticket/11767" target="_top">#11767</a>).
        </li>
<li class="listitem">
          Regenerated certificates used by SSL examples.
        </li>
<li class="listitem">
          Fixed buffer sizes passed to <code class="computeroutput"><span class="identifier">strncat</span></code>
          in the <code class="computeroutput"><span class="identifier">getaddrinfo</span></code> emulation
          and in the SSL wrapper's password handling.
        </li>
<li class="listitem">
          Changed Windows backend to use non-macro <code class="computeroutput"><span class="identifier">CreateEventW</span></code>
          rather than <code class="computeroutput"><span class="identifier">CreateEvent</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/11732" target="_top">#11732</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h37"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_6___boost_1_58"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_6___boost_1_58">Asio
      1.10.6 / Boost 1.58</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Ensured errors generated by Windows' <code class="computeroutput"><span class="identifier">ConnectEx</span></code>
          function are mapped to their portable equivalents (<a href="https://svn.boost.org/trac/boost/ticket/10744" target="_top">#10744</a>).
        </li>
<li class="listitem">
          Added new macro <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_CONNECTEX</span></code>
          to allow use of <code class="computeroutput"><span class="identifier">ConnectEx</span></code>
          to be explicitly disabled.
        </li>
<li class="listitem">
          Fixed a race condition in <code class="computeroutput"><span class="identifier">windows</span><span class="special">::</span><span class="identifier">object_handle</span></code>
          when there are pending wait operations on destruction (<a href="https://svn.boost.org/trac/boost/ticket/10624" target="_top">#10624</a>).
        </li>
<li class="listitem">
          Fixed IPv6 address parsing on FreeBSD, where a trailing scope ID would
          cause conversion to fail with <code class="computeroutput"><span class="identifier">EINVAL</span></code>.
        </li>
<li class="listitem">
          Worked around shared library visibility issues by ensuring Asio types use
          default visibility (<a href="https://svn.boost.org/trac/boost/ticket/9465" target="_top">#9465</a>, <a href="https://svn.boost.org/trac/boost/ticket/11070" target="_top">#11070</a>).
        </li>
<li class="listitem">
          Changed the SSL wrapper to call the password callback when loading an in-memory
          key (<a href="https://svn.boost.org/trac/boost/ticket/10828" target="_top">#10828</a>).
        </li>
<li class="listitem">
          Fixed false SSL error reports by ensuring that the SSL error queue is cleared
          prior to each operation.
        </li>
<li class="listitem">
          Fixed an <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code>
          bug that may result in spurious 'short read' errors.
        </li>
<li class="listitem">
          Removed a redundant null pointer check in the SSL engine (<a href="https://svn.boost.org/trac/boost/ticket/10088" target="_top">#10088</a>).
        </li>
<li class="listitem">
          Added options for disabling TLS v1.1 and v1.2 (<a href="https://svn.boost.org/trac/boost/ticket/10690" target="_top">#10690</a>).
        </li>
<li class="listitem">
          Removed use of deprecated OpenSSL function <code class="computeroutput"><span class="identifier">ERR_remove_state</span></code>.
        </li>
<li class="listitem">
          Fixed detection of various C++11 features with Clang (<a href="https://svn.boost.org/trac/boost/ticket/8835" target="_top">#8835</a>, <a href="https://svn.boost.org/trac/boost/ticket/10884" target="_top">#10884</a>).
        </li>
<li class="listitem">
          Fixed detection of C++11 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">addressof</span></code>
          with <code class="literal">g++</code> (<a href="https://svn.boost.org/trac/boost/ticket/10982" target="_top">#10982</a>).
        </li>
<li class="listitem">
          Changed multicast test to treat certain <code class="computeroutput"><span class="identifier">join_group</span></code>
          failures as non-fatal.
        </li>
<li class="listitem">
          Decoupled Asio unit tests from Boost.Test (<a href="https://svn.boost.org/trac/boost/ticket/11116" target="_top">#11116</a>).
        </li>
<li class="listitem">
          Changed the tutorial to use <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span></code>
          to ensure output is flushed.
        </li>
<li class="listitem">
          Fixed an unsigned integer overflow reported by Clang's integer sanitizer.
        </li>
<li class="listitem">
          Added support for move-only return types when using a <code class="computeroutput"><span class="identifier">yield_context</span></code>
          object with asynchronous operations.
        </li>
<li class="listitem">
          Changed <code class="computeroutput"><span class="identifier">yield_context</span></code> to
          allow reentrant calls to the completion handler from an initiating function.
        </li>
<li class="listitem">
          Updated detection of Windows Runtime to work with latest Windows SDK.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h38"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_5___boost_1_57"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_5___boost_1_57">Asio
      1.10.5 / Boost 1.57</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed the <code class="literal">kqueue</code> reactor so that it works on FreeBSD
          (<a href="https://svn.boost.org/trac/boost/ticket/10606" target="_top">#10606</a>).
        </li>
<li class="listitem">
          Fixed an issue in the <code class="literal">kqueue</code> reactor which resulted
          in spinning when using serial ports on Mac OS (<a href="https://svn.boost.org/trac/boost/ticket/10496" target="_top">#10496</a>).
        </li>
<li class="listitem">
          Fixed <code class="literal">kqueue</code> reactor support for read-only file descriptors
          (<a href="https://svn.boost.org/trac/boost/ticket/10367" target="_top">#10367</a>).
        </li>
<li class="listitem">
          Fixed a compile error when using the <code class="literal">/dev/poll</code> reactor
          (<a href="https://svn.boost.org/trac/boost/ticket/10350" target="_top">#10350</a>, <a href="https://svn.boost.org/trac/boost/ticket/10572" target="_top">#10572</a>).
        </li>
<li class="listitem">
          Changed the Windows backend to use <code class="computeroutput"><span class="identifier">WSASocketW</span></code>,
          as <code class="computeroutput"><span class="identifier">WSASocketA</span></code> has been
          deprecated (<a href="https://svn.boost.org/trac/boost/ticket/10534" target="_top">#10534</a>).
        </li>
<li class="listitem">
          Fixed some warnings reported by Visual C++ 2013 (<a href="https://svn.boost.org/trac/boost/ticket/10376" target="_top">#10376</a>).
        </li>
<li class="listitem">
          Fixed integer type used in the WinRT version of the byte-order conversion
          functions (<a href="https://svn.boost.org/trac/boost/ticket/10539" target="_top">#10539</a>).
        </li>
<li class="listitem">
          Changed documentation to indicate that <code class="computeroutput"><span class="identifier">use_future</span></code>
          and <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code>
          are not made available when including the <code class="computeroutput"><span class="identifier">asio</span><span class="special">.</span><span class="identifier">hpp</span></code>
          convenience header (<a href="https://svn.boost.org/trac/boost/ticket/10567" target="_top">#10567</a>).
        </li>
<li class="listitem">
          Explicitly marked <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">strand</span></code>
          as deprecated. Use <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">strand</span></code>
          instead.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h39"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_4___boost_1_56"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_4___boost_1_56">Asio
      1.10.4 / Boost 1.56</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Stopped using certain Winsock functions that are marked as deprecated in
          the latest Visual C++ and Windows SDK.
        </li>
<li class="listitem">
          Fixed a shadow variable warning on Windows.
        </li>
<li class="listitem">
          Fixed a regression in the <code class="literal">kqueue</code> backend that was introduced
          in Asio 1.10.2.
        </li>
<li class="listitem">
          Added a workaround for building the unit tests with <code class="literal">gcc</code>
          on AIX.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h40"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_3"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_3">Asio
      1.10.3</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Worked around a <code class="literal">gcc</code> problem to do with anonymous enums
          (<a href="https://svn.boost.org/trac/boost/ticket/10042" target="_top">#10042</a>).
        </li>
<li class="listitem">
          Reverted the Windows <code class="computeroutput"><span class="identifier">HANDLE</span></code>
          backend change to ignore <code class="computeroutput"><span class="identifier">ERROR_MORE_DATA</span></code>.
          Instead, the error will be propagated as with any other (i.e. in an <code class="computeroutput"><span class="identifier">error_code</span></code> or thrown as a <code class="computeroutput"><span class="identifier">system_error</span></code>), and the number of bytes
          transferred will be returned. For code that needs to handle partial messages,
          the <code class="computeroutput"><span class="identifier">error_code</span></code> overload
          should be used (<a href="https://svn.boost.org/trac/boost/ticket/10034" target="_top">#10034</a>).
        </li>
<li class="listitem">
          Fixed an off-by-one error in the <code class="computeroutput"><span class="identifier">signal_set</span></code>
          implementation's signal number check (<a href="https://svn.boost.org/trac/boost/ticket/9324" target="_top">#9324</a>).
        </li>
<li class="listitem">
          Changed the Windows IOCP backend to not assume that <code class="computeroutput"><span class="identifier">SO_UPDATE_CONNECT_CONTEXT</span></code>
          is defined (<a href="https://svn.boost.org/trac/boost/ticket/10016" target="_top">#10016</a>).
        </li>
<li class="listitem">
          Fixed a Windows-specific issue, introduced in Asio 1.10.2, by using <code class="computeroutput"><span class="identifier">VerifyVersionInfo</span></code> rather than <code class="computeroutput"><span class="identifier">GetVersionEx</span></code>, as <code class="computeroutput"><span class="identifier">GetVersionEx</span></code>
          has been deprecated.
        </li>
<li class="listitem">
          Changed to use SSE2 intrinsics rather than inline assembly, to allow the
          Cray compiler to work.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h41"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_2"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_2">Asio
      1.10.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">spawn</span><span class="special">()</span></code>
          to work correctly with new Boost.Coroutine interface (<a href="https://svn.boost.org/trac/boost/ticket/9442" target="_top">#9442</a>, <a href="https://svn.boost.org/trac/boost/ticket/9928" target="_top">#9928</a>).
        </li>
<li class="listitem">
          Ensured that incomplete <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">spawn</span><span class="special">()</span></code> coroutines are correctly unwound when
          cleaned up by the <code class="computeroutput"><span class="identifier">io_service</span></code>
          destructor (<a href="https://svn.boost.org/trac/boost/ticket/9731" target="_top">#9731</a>).
        </li>
<li class="listitem">
          Fixed delegation of continuation hook for handlers produced by <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">wrap</span><span class="special">()</span></code>
          and <code class="computeroutput"><span class="identifier">strand</span><span class="special">::</span><span class="identifier">wrap</span><span class="special">()</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/9741" target="_top">#9741</a>).
        </li>
<li class="listitem">
          Changed the Windows I/O completion port backend to use <code class="computeroutput"><span class="identifier">ConnectEx</span></code>,
          if available, for connection-oriented IP sockets.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">io_service</span></code>
          backend for non-Windows (and non-IOCP Windows) platforms to use a single
          condition variable per <code class="computeroutput"><span class="identifier">io_service</span></code>
          instance. This addresses a potential race condition when <code class="computeroutput"><span class="identifier">run_one</span><span class="special">()</span></code>
          is used from multiple threads.
        </li>
<li class="listitem">
          Prevented integer overflow when computing timeouts based on some <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span></code> and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span></code>
          clocks (<a href="https://svn.boost.org/trac/boost/ticket/9662" target="_top">#9662</a>, <a href="https://svn.boost.org/trac/boost/ticket/9778" target="_top">#9778</a>).
        </li>
<li class="listitem">
          Made further changes to <code class="computeroutput"><span class="identifier">EV_CLEAR</span></code>
          handling in the kqueue backend, to address other cases where the <code class="computeroutput"><span class="identifier">close</span><span class="special">()</span></code>
          system call may hang on Mac OS X.
        </li>
<li class="listitem">
          Fixed infinite recursion in implementation of <code class="computeroutput"><span class="identifier">resolver_query_base</span><span class="special">::</span><span class="identifier">flags</span><span class="special">::</span><span class="keyword">operator</span><span class="special">~</span></code> (<a href="https://svn.boost.org/trac/boost/ticket/9548" target="_top">#9548</a>).
        </li>
<li class="listitem">
          Made the <code class="computeroutput"><span class="identifier">select</span></code> reactor
          more efficient on Windows for large numbers of sockets (<a href="https://svn.boost.org/trac/boost/ticket/9528" target="_top">#9528</a>).
        </li>
<li class="listitem">
          Fixed a Windows-specific type-aliasing issue reported by <code class="literal">gcc</code>
          (<a href="https://svn.boost.org/trac/boost/ticket/9550" target="_top">#9550</a>).
        </li>
<li class="listitem">
          Prevented execution of compile-time-only buffer test to avoid triggering
          an address sanitiser warning (<a href="https://svn.boost.org/trac/boost/ticket/8295" target="_top">#8295</a>).
        </li>
<li class="listitem">
          Disabled the <code class="computeroutput"><span class="identifier">GetQueuedCompletionStatus</span></code>
          timeout workaround on recent versions of Windows.
        </li>
<li class="listitem">
          Added support for string-based scope IDs when using link-local multicast
          addresses.
        </li>
<li class="listitem">
          Changed IPv6 multicast group join to use the address's scope ID as the
          interface, if an interface is not explicitly specified.
        </li>
<li class="listitem">
          Fixed multicast test failure on Mac OS X and the BSDs by using a link-local
          multicast address.
        </li>
<li class="listitem">
          Various minor documentation improvements (<a href="https://svn.boost.org/trac/boost/ticket/8295" target="_top">#8295</a>, <a href="https://svn.boost.org/trac/boost/ticket/9605" target="_top">#9605</a>, <a href="https://svn.boost.org/trac/boost/ticket/9771" target="_top">#9771</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h42"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_1___boost_1_55"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_1___boost_1_55">Asio
      1.10.1 / Boost 1.55</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Implemented a limited port to Windows Runtime. This support requires that
          the language extensions be enabled. Due to the restricted facilities exposed
          by the Windows Runtime API, the port also comes with the following caveats:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                The core facilities such as the <code class="computeroutput"><span class="identifier">io_service</span></code>,
                <code class="computeroutput"><span class="identifier">strand</span></code>, buffers,
                composed operations, timers, etc., should all work as normal.
              </li>
<li class="listitem">
                For sockets, only client-side TCP is supported.
              </li>
<li class="listitem">
                Explicit binding of a client-side TCP socket is not supported.
              </li>
<li class="listitem">
                The <code class="computeroutput"><span class="identifier">cancel</span><span class="special">()</span></code>
                function is not supported for sockets. Asynchronous operations may
                only be cancelled by closing the socket.
              </li>
<li class="listitem">
                Operations that use <code class="computeroutput"><span class="identifier">null_buffers</span></code>
                are not supported.
              </li>
<li class="listitem">
                Only <code class="computeroutput"><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">no_delay</span></code> and <code class="computeroutput"><span class="identifier">socket_base</span><span class="special">::</span><span class="identifier">keep_alive</span></code>
                options are supported.
              </li>
<li class="listitem">
                Resolvers do not support service names, only numbers. I.e. you must
                use "80" rather than "http".
              </li>
<li class="listitem">
                Most resolver query flags have no effect.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a regression (introduced in Boost 1.54) where, on some platforms,
          errors from <code class="computeroutput"><span class="identifier">async_connect</span></code>
          were not correctly propagated through to the completion handler (<a href="https://svn.boost.org/trac/boost/ticket/8795" target="_top">#8795</a>).
        </li>
<li class="listitem">
          Fixed a Windows-specific regression (introduced in Boost 1.54) that occurs
          when multiple threads are running an <code class="computeroutput"><span class="identifier">io_service</span></code>.
          When the bug occurs, the result of an asynchronous operation (error and
          bytes tranferred) is incorrectly discarded and zero values used instead.
          For TCP sockets this results in spurious end-of-file notifications (<a href="https://svn.boost.org/trac/boost/ticket/8933" target="_top">#8933</a>).
        </li>
<li class="listitem">
          Fixed a bug in handler tracking, where it was not correctly printing out
          some handler IDs (<a href="https://svn.boost.org/trac/boost/ticket/8808" target="_top">#8808</a>).
        </li>
<li class="listitem">
          Fixed the comparison used to test for successful synchronous accept operations
          so that it works correctly with unsigned socket descriptors (<a href="https://svn.boost.org/trac/boost/ticket/8752" target="_top">#8752</a>).
        </li>
<li class="listitem">
          Ensured the signal number is correctly passed to the completion handler
          when starting an <code class="computeroutput"><span class="identifier">async_wait</span></code>
          on a signal that is already raised (<a href="https://svn.boost.org/trac/boost/ticket/8738" target="_top">#8738</a>).
        </li>
<li class="listitem">
          Suppressed a g++ 4.8+ warning about unused typedefs (<a href="https://svn.boost.org/trac/boost/ticket/8980" target="_top">#8980</a>).
        </li>
<li class="listitem">
          Enabled the move optimisation for handlers that use the default invocation
          hook (<a href="https://svn.boost.org/trac/boost/ticket/8624" target="_top">#8624</a>).
        </li>
<li class="listitem">
          Clarified that programs must not issue overlapping <code class="computeroutput"><span class="identifier">async_write_at</span></code>
          operations (<a href="https://svn.boost.org/trac/boost/ticket/8669" target="_top">#8669</a>).
        </li>
<li class="listitem">
          Changed the Windows <code class="computeroutput"><span class="identifier">HANDLE</span></code>
          backend to treat <code class="computeroutput"><span class="identifier">ERROR_MORE_DATA</span></code>
          as a non-fatal error when returned by <code class="computeroutput"><span class="identifier">GetOverlappedResult</span></code>
          for a synchronous read (<a href="https://svn.boost.org/trac/boost/ticket/8722" target="_top">#8722</a>).
        </li>
<li class="listitem">
          Visual C++ language extensions use <code class="computeroutput"><span class="identifier">generic</span></code>
          as a keyword. Added a workaround that renames the namespace to <code class="computeroutput"><span class="identifier">cpp_generic</span></code> when those language extensions
          are in effect.
        </li>
<li class="listitem">
          Fixed some asynchronous operations that missed out on getting <code class="computeroutput"><span class="identifier">async_result</span></code> support in Boost 1.54. In
          particular, the buffered stream templates have been updated so that they
          adhere to current handler patterns (<a href="https://svn.boost.org/trac/boost/ticket/9000" target="_top">#9000</a>, <a href="https://svn.boost.org/trac/boost/ticket/9001" target="_top">#9001</a>).
        </li>
<li class="listitem">
          Enabled move support for Microsoft Visual Studio 2012 (<a href="https://svn.boost.org/trac/boost/ticket/8959" target="_top">#8959</a>).
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="identifier">use_future</span></code> support
          for Microsoft Visual Studio 2012.
        </li>
<li class="listitem">
          Removed a use of <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">min</span></code> in the Windows IOCP backend to avoid
          a dependency on the <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">algorithm</span><span class="special">&gt;</span></code> header (<a href="https://svn.boost.org/trac/boost/ticket/8758" target="_top">#8758</a>).
        </li>
<li class="listitem">
          Eliminated some unnecessary handler copies.
        </li>
<li class="listitem">
          Fixed support for older versions of OpenSSL that do not provide the <code class="computeroutput"><span class="identifier">SSL_CTX_clear_options</span></code> function (<a href="https://svn.boost.org/trac/boost/ticket/9273" target="_top">#9273</a>).
        </li>
<li class="listitem">
          Fixed various minor and cosmetic issues in code and documentation (including
          <a href="https://svn.boost.org/trac/boost/ticket/8347" target="_top">#8347</a>, <a href="https://svn.boost.org/trac/boost/ticket/8950" target="_top">#8950</a>, <a href="https://svn.boost.org/trac/boost/ticket/8953" target="_top">#8953</a>, <a href="https://svn.boost.org/trac/boost/ticket/8965" target="_top">#8965</a>, <a href="https://svn.boost.org/trac/boost/ticket/8997" target="_top">#8997</a>, <a href="https://svn.boost.org/trac/boost/ticket/9230" target="_top">#9230</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h43"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_10_0___boost_1_54"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_10_0___boost_1_54">Asio
      1.10.0 / Boost 1.54</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added new traits classes, <code class="computeroutput"><span class="identifier">handler_type</span></code>
          and <code class="computeroutput"><span class="identifier">async_result</span></code>, that
          allow the customisation of the return type of an initiating function.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">spawn</span><span class="special">()</span></code>
          function, a high-level wrapper for running stackful coroutines, based on
          the Boost.Coroutine library. The <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code> function enables programs to implement
          asynchronous logic in a synchronous manner. For example: <code class="computeroutput"><span class="identifier">size_t</span> <span class="identifier">n</span>
          <span class="special">=</span> <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span> <span class="identifier">yield</span><span class="special">);</span></code>. For further information, see <a class="link" href="overview/composition/spawn.html" title="Stackful Coroutines">Stackful
          Coroutines</a>.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span></code> special value, which provides
          first-class support for returning a C++11 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">future</span></code>
          from an asynchronous operation's initiating function. For example: <code class="computeroutput"><span class="identifier">future</span><span class="special">&lt;</span><span class="identifier">size_t</span><span class="special">&gt;</span>
          <span class="special">=</span> <span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">use_future</span><span class="special">);</span></code>. For further information, see <a class="link" href="overview/composition/futures.html" title="Futures">Futures</a>.
        </li>
<li class="listitem">
          Promoted the stackless coroutine class and macros to be part of Asio's
          documented interface, rather than part of the HTTP server 4 example. For
          further information, see <a class="link" href="overview/composition/coroutine.html" title="Stackless Coroutines">Stackless
          Coroutines</a>.
        </li>
<li class="listitem">
          Added a new handler hook called <code class="computeroutput"><span class="identifier">asio_handler_is_continuation</span></code>.
          Asynchronous operations may represent a continuation of the asynchronous
          control flow associated with the current executing handler. The <code class="computeroutput"><span class="identifier">asio_handler_is_continuation</span></code> hook can
          be customised to return <code class="computeroutput"><span class="keyword">true</span></code>
          if this is the case, and Asio's implementation can use this knowledge to
          optimise scheduling of the new handler. To cover common cases, Asio customises
          the hook for strands, <code class="computeroutput"><span class="identifier">spawn</span><span class="special">()</span></code> and composed asynchronous operations.
        </li>
<li class="listitem">
          Added four new generic protocol classes, <code class="computeroutput"><span class="identifier">generic</span><span class="special">::</span><span class="identifier">datagram_protocol</span></code>,
          <code class="computeroutput"><span class="identifier">generic</span><span class="special">::</span><span class="identifier">raw_protocol</span></code>, <code class="computeroutput"><span class="identifier">generic</span><span class="special">::</span><span class="identifier">seq_packet_protocol</span></code>
          and <code class="computeroutput"><span class="identifier">generic</span><span class="special">::</span><span class="identifier">stream_protocol</span></code>, which implement the
          <code class="computeroutput"><span class="identifier">Protocol</span></code> type requirements,
          but allow the user to specify the address family (e.g. <code class="computeroutput"><span class="identifier">AF_INET</span></code>)
          and protocol type (e.g. <code class="computeroutput"><span class="identifier">IPPROTO_TCP</span></code>)
          at runtime. For further information, see <a class="link" href="overview/networking/other_protocols.html" title="Support for Other Protocols">Support
          for Other Protocols</a>.
        </li>
<li class="listitem">
          Added C++11 move constructors that allow the conversion of a socket (or
          acceptor) into a more generic type. For example, an <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span></code>
          can be converted into a <code class="computeroutput"><span class="identifier">generic</span><span class="special">::</span><span class="identifier">stream_protocol</span><span class="special">::</span><span class="identifier">socket</span></code>
          via move construction. For further information, see <a class="link" href="overview/networking/other_protocols.html" title="Support for Other Protocols">Support
          for Other Protocols</a>.
        </li>
<li class="listitem">
          Extended the <code class="computeroutput"><span class="identifier">basic_socket_acceptor</span><span class="special">&lt;&gt;</span></code>'s <code class="computeroutput"><span class="identifier">accept</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">async_accept</span><span class="special">()</span></code> functions to allow a new connection to
          be accepted directly into a socket of a more generic type. For example,
          an <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">acceptor</span></code> can be used to accept into a
          <code class="computeroutput"><span class="identifier">generic</span><span class="special">::</span><span class="identifier">stream_protocol</span><span class="special">::</span><span class="identifier">socket</span></code> object. For further information,
          see <a class="link" href="overview/networking/other_protocols.html" title="Support for Other Protocols">Support
          for Other Protocols</a>.
        </li>
<li class="listitem">
          Moved existing examples into a C++03-specific directory, and added a new
          directory for C++11-specific examples. A limited subset of the C++03 examples
          have been converted to their C++11 equivalents.
        </li>
<li class="listitem">
          Various SSL enhancements. Thanks go to Nick Jones, on whose work these
          changes are based.
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Added support for SSL handshakes with re-use of data already read
                from the wire. New overloads of the <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code> class's <code class="computeroutput"><span class="identifier">handshake</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">async_handshake</span><span class="special">()</span></code> functions have been added. These
                accept a <code class="computeroutput"><span class="identifier">ConstBufferSequence</span></code>
                to be used as initial input to the ssl engine for the handshake procedure.
              </li>
<li class="listitem">
                Added support for creation of TLSv1.1 and TLSv1.2 <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span></code>
                objects.
              </li>
<li class="listitem">
                Added a <code class="computeroutput"><span class="identifier">set_verify_depth</span><span class="special">()</span></code> function to the <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span></code>
                and <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;&gt;</span></code>
                classes.
              </li>
<li class="listitem">
                Added the ability to load SSL certificate and key data from memory
                buffers. New functions, <code class="computeroutput"><span class="identifier">add_certificate_authority</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">use_certificate</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">use_certificate_chain</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">use_private_key</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">use_rsa_private_key</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">use_tmp_dh</span><span class="special">()</span></code>, have been added to the <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span></code> class.
              </li>
<li class="listitem">
                Changed <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span></code> to automatically disable
                SSL compression by default. To enable, use the new <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">clear_options</span><span class="special">()</span></code>
                function, as in <code class="computeroutput"><span class="identifier">my_context</span><span class="special">.</span><span class="identifier">clear_options</span><span class="special">(</span><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">no_compression</span><span class="special">)</span></code>.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a potential deadlock in <code class="computeroutput"><span class="identifier">signal_set</span></code>
          implementation.
        </li>
<li class="listitem">
          Fixed an error in acceptor example in documentation <a href="https://svn.boost.org/trac/boost/ticket/8421" target="_top">#8421</a>.
        </li>
<li class="listitem">
          Fixed copy-paste errors in waitable timer documentation <a href="https://svn.boost.org/trac/boost/ticket/8602" target="_top">#8602</a>.
        </li>
<li class="listitem">
          Added assertions to satisfy some code analysis tools <a href="https://svn.boost.org/trac/boost/ticket/7739" target="_top">#7739</a>.
        </li>
<li class="listitem">
          Fixed a malformed <code class="computeroutput"><span class="preprocessor">#warning</span></code>
          directive <a href="https://svn.boost.org/trac/boost/ticket/7939" target="_top">#7939</a>.
        </li>
<li class="listitem">
          Fixed a potential data race in the Linux <code class="computeroutput"><span class="identifier">epoll</span></code>
          implementation.
        </li>
<li class="listitem">
          Fixed a Windows-specific bug, where certain operations might generate an
          <code class="computeroutput"><span class="identifier">error_code</span></code> with an invalid
          (i.e. <code class="computeroutput"><span class="identifier">NULL</span></code>) <code class="computeroutput"><span class="identifier">error_category</span></code> <a href="https://svn.boost.org/trac/boost/ticket/8613" target="_top">#8613</a>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">basic_waitable_timer</span></code>'s
          underlying implementation so that it can handle any <code class="computeroutput"><span class="identifier">time_point</span></code>
          value without overflowing the intermediate duration objects.
        </li>
<li class="listitem">
          Fixed a problem with lost thread wakeups that can occur when making concurrent
          calls to <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code>
          and <code class="computeroutput"><span class="identifier">poll</span><span class="special">()</span></code>
          on the same <code class="computeroutput"><span class="identifier">io_service</span></code>
          object <a href="https://svn.boost.org/trac/boost/ticket/8354" target="_top">#8354</a>.
        </li>
<li class="listitem">
          Fixed implementation of asynchronous connect operation so that it can cope
          with spurious readiness notifications from the reactor <a href="https://svn.boost.org/trac/boost/ticket/7961" target="_top">#7961</a>.
        </li>
<li class="listitem">
          Fixed a memory leak in the <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">rfc2818_verification</span></code>
          class.
        </li>
<li class="listitem">
          Added a mechanism for disabling automatic Winsock initialisation <a href="https://svn.boost.org/trac/boost/ticket/3605" target="_top">#3605</a>.
          See the header file <code class="literal">boost/asio/detail/winsock_init.hpp</code>
          for details.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h44"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_8_3___boost_1_53"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_8_3___boost_1_53">Asio
      1.8.3 / Boost 1.53</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed some 64-to-32-bit conversion warnings (<a href="https://svn.boost.org/trac/boost/ticket/7459" target="_top">#7459</a>).
        </li>
<li class="listitem">
          Fixed some small errors in documentation and comments (<a href="https://svn.boost.org/trac/boost/ticket/7761" target="_top">#7761</a>).
        </li>
<li class="listitem">
          Fixed an error in the example embedded in <code class="computeroutput"><span class="identifier">basic_socket</span><span class="special">::</span><span class="identifier">get_option</span></code>'s
          documentation (<a href="https://svn.boost.org/trac/boost/ticket/7562" target="_top">#7562</a>).
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="keyword">long</span></code> rather
          than <code class="computeroutput"><span class="keyword">int</span></code> for SSL_CTX options,
          to match OpenSSL (<a href="https://svn.boost.org/trac/boost/ticket/7209" target="_top">#7209</a>).
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="identifier">_snwprintf</span></code>
          to address a compile error due to the changed <code class="computeroutput"><span class="identifier">swprintf</span></code>
          signature in recent versions of MinGW (<a href="https://svn.boost.org/trac/boost/ticket/7373" target="_top">#7373</a>).
        </li>
<li class="listitem">
          Fixed a deadlock that can occur on Windows when shutting down a pool of
          <code class="computeroutput"><span class="identifier">io_service</span></code> threads due
          to running out of work (<a href="https://svn.boost.org/trac/boost/ticket/7552" target="_top">#7552</a>).
        </li>
<li class="listitem">
          Enabled the <code class="computeroutput"><span class="keyword">noexcept</span></code> qualifier
          for error categories (<a href="https://svn.boost.org/trac/boost/ticket/7797" target="_top">#7797</a>).
        </li>
<li class="listitem">
          Changed UNIX domain socket example to treat errors from <code class="computeroutput"><span class="identifier">accept</span></code>
          as non-fatal (<a href="https://svn.boost.org/trac/boost/ticket/7488" target="_top">#7488</a>).
        </li>
<li class="listitem">
          Added a small block recycling optimisation to improve default memory allocation
          behaviour.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h45"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_8_2___boost_1_51"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_8_2___boost_1_51">Asio
      1.8.2 / Boost 1.51</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed an incompatibility between <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">iostream</span></code>
          and C++11 (<a href="https://svn.boost.org/trac/boost/ticket/7162" target="_top">#7162</a>).
        </li>
<li class="listitem">
          Decorated GCC attribute names with underscores to prevent interaction with
          user-defined macros (<a href="https://svn.boost.org/trac/boost/ticket/6415" target="_top">#6415</a>).
        </li>
<li class="listitem">
          Added missing <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">cctype</span><span class="special">&gt;</span></code>, needed for some versions of MinGW.
        </li>
<li class="listitem">
          Changed to use <code class="literal">gcc</code>'s atomic builtins on ARM CPUs, when
          available (<a href="https://svn.boost.org/trac/boost/ticket/7140" target="_top">#7140</a>).
        </li>
<li class="listitem">
          Changed strand destruction to be a no-op, to allow strand objects to be
          destroyed after their associated <code class="computeroutput"><span class="identifier">io_service</span></code>
          has been destroyed.
        </li>
<li class="listitem">
          Added support for some newer versions of glibc which provide the <code class="computeroutput"><span class="identifier">epoll_create1</span><span class="special">()</span></code>
          function but always fail with <code class="computeroutput"><span class="identifier">ENOSYS</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/7012" target="_top">#7012</a>).
        </li>
<li class="listitem">
          Changed the SSL implementation to throw an exception if SSL engine initialisation
          fails (<a href="https://svn.boost.org/trac/boost/ticket/6303" target="_top">#6303</a>).
        </li>
<li class="listitem">
          Fixed another regression in <code class="computeroutput"><span class="identifier">buffered_write_stream</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/6310" target="_top">#6310</a>).
        </li>
<li class="listitem">
          Implemented various minor performance improvements, primarily targeted
          at Linux x86 and x86-64 platforms.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h46"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_8_1___boost_1_50"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_8_1___boost_1_50">Asio
      1.8.1 / Boost 1.50</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">epoll_reactor</span></code>
          backend to do lazy registration for <code class="computeroutput"><span class="identifier">EPOLLOUT</span></code>
          events.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">epoll_reactor</span></code>
          handling of out-of-band data, which was broken by an incomplete fix in
          the last release.
        </li>
<li class="listitem">
          Changed Asio's SSL wrapper to respect OpenSSL's <code class="computeroutput"><span class="identifier">OPENSSL_NO_ENGINE</span></code>
          feature test <code class="computeroutput"><span class="preprocessor">#define</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/6432" target="_top">#6432</a>).
        </li>
<li class="listitem">
          Fixed <code class="computeroutput"><span class="identifier">windows</span><span class="special">::</span><span class="identifier">object_handle</span></code> so that it works with Windows
          compilers that support C++11 move semantics (such as <code class="literal">g++</code>).
        </li>
<li class="listitem">
          Improved the performance of strand rescheduling.
        </li>
<li class="listitem">
          Added support for <code class="literal">g++</code> 4.7 when compiling in C++11 mode
          (<a href="https://svn.boost.org/trac/boost/ticket/6620" target="_top">#6620</a>).
        </li>
<li class="listitem">
          Fixed a problem where <code class="computeroutput"><span class="identifier">signal_set</span></code>
          handlers were not being delivered when the <code class="computeroutput"><span class="identifier">io_service</span></code>
          was constructed with a <code class="computeroutput"><span class="identifier">concurrency_hint</span></code>
          of 1 (<a href="https://svn.boost.org/trac/boost/ticket/6657" target="_top">#6657</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h47"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_8_0___boost_1_49"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_8_0___boost_1_49">Asio
      1.8.0 / Boost 1.49</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added a new class template <code class="computeroutput"><span class="identifier">basic_waitable_timer</span></code>
          based around the C++11 clock type requirements. It may be used with the
          clocks from the C++11 <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">chrono</span><span class="special">&gt;</span></code>
          library facility or, if those are not available, Boost.Chrono. The typedefs
          <code class="computeroutput"><span class="identifier">high_resolution_timer</span></code>,
          <code class="computeroutput"><span class="identifier">steady_timer</span></code> and <code class="computeroutput"><span class="identifier">system_timer</span></code> may be used to create timer
          objects for the standard clock types.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">windows</span><span class="special">::</span><span class="identifier">object_handle</span></code> class for performing waits
          on Windows kernel objects. Thanks go to Boris Schaeling for contributing
          substantially to the development of this feature.
        </li>
<li class="listitem">
          On Linux, <code class="computeroutput"><span class="identifier">connect</span><span class="special">()</span></code>
          can return EAGAIN in certain circumstances. Remapped this to another error
          so that it doesn't look like a non-blocking operation (<a href="https://svn.boost.org/trac/boost/ticket/6048" target="_top">#6048</a>).
        </li>
<li class="listitem">
          Fixed a compile error on NetBSD (<a href="https://svn.boost.org/trac/boost/ticket/6098" target="_top">#6098</a>).
        </li>
<li class="listitem">
          Fixed deadlock on Mac OS X (<a href="https://svn.boost.org/trac/boost/ticket/6275" target="_top">#6275</a>).
        </li>
<li class="listitem">
          Fixed a regression in <code class="computeroutput"><span class="identifier">buffered_write_stream</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/6310" target="_top">#6310</a>).
        </li>
<li class="listitem">
          Fixed a non-paged pool "leak" on Windows when an <code class="computeroutput"><span class="identifier">io_service</span></code> is repeatedly run without
          anything to do (<a href="https://svn.boost.org/trac/boost/ticket/6321" target="_top">#6321</a>).
        </li>
<li class="listitem">
          Reverted earlier change to allow some speculative operations to be performed
          without holding the lock, as it introduced a race condition in some multithreaded
          scenarios.
        </li>
<li class="listitem">
          Fixed a bug where the second buffer in an array of two buffers may be ignored
          if the first buffer is empty.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h48"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_6_1___boost_1_48"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_6_1___boost_1_48">Asio
      1.6.1 / Boost 1.48</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Implemented various performance improvements, including:
          <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
                Using thread-local operation queues in single-threaded use cases
                (i.e. when <code class="computeroutput"><span class="identifier">concurrency_hint</span></code>
                is 1) to eliminate a lock/unlock pair.
              </li>
<li class="listitem">
                Allowing some <code class="computeroutput"><span class="identifier">epoll_reactor</span></code>
                speculative operations to be performed without holding the lock.
              </li>
<li class="listitem">
                Improving locality of reference by performing an <code class="computeroutput"><span class="identifier">epoll_reactor</span></code>'s
                I/O operation immediately before the corresponding handler is called.
                This also improves scalability across CPUs when multiple threads
                are running the <code class="computeroutput"><span class="identifier">io_service</span></code>.
              </li>
<li class="listitem">
                Specialising asynchronous read and write operations for buffer sequences
                that are arrays (<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span></code>
                or <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">array</span></code>) of exactly two buffers.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a compile error in the regex overload of <code class="computeroutput"><span class="identifier">async_read_until</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/5688" target="_top">#5688</a>).
        </li>
<li class="listitem">
          Fixed a Windows-specific compile error by explicitly specifying the <code class="computeroutput"><span class="identifier">signal</span><span class="special">()</span></code>
          function from the global namespace (<a href="https://svn.boost.org/trac/boost/ticket/5722" target="_top">#5722</a>).
        </li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">deadline_timer</span></code>
          implementation so that it does not read the clock unless the timer heap
          is non-empty.
        </li>
<li class="listitem">
          Changed the SSL stream's buffers' sizes so that they are large enough to
          hold a complete TLS record (<a href="https://svn.boost.org/trac/boost/ticket/5854" target="_top">#5854</a>).
        </li>
<li class="listitem">
          Fixed the behaviour of the synchronous <code class="computeroutput"><span class="identifier">null_buffers</span></code>
          operations so that they obey the user's non-blocking setting (<a href="https://svn.boost.org/trac/boost/ticket/5756" target="_top">#5756</a>).
        </li>
<li class="listitem">
          Changed to set the size of the select <code class="computeroutput"><span class="identifier">fd_set</span></code>
          at runtime when using Windows.
        </li>
<li class="listitem">
          Disabled an MSVC warning due to const qualifier being applied to function
          type.
        </li>
<li class="listitem">
          Fixed a crash that occurs when using the Intel C++ compiler (<a href="https://svn.boost.org/trac/boost/ticket/5763" target="_top">#5763</a>).
        </li>
<li class="listitem">
          Changed the initialisation of the OpenSSL library so that it supports all
          available algorithms.
        </li>
<li class="listitem">
          Fixed the SSL error mapping used when the session is gracefully shut down.
        </li>
<li class="listitem">
          Added some latency test programs.
        </li>
<li class="listitem">
          Clarified that a read operation ends when the buffer is full (<a href="https://svn.boost.org/trac/boost/ticket/5999" target="_top">#5999</a>).
        </li>
<li class="listitem">
          Fixed an exception safety issue in <code class="computeroutput"><span class="identifier">epoll_reactor</span></code>
          initialisation (<a href="https://svn.boost.org/trac/boost/ticket/6006" target="_top">#6006</a>).
        </li>
<li class="listitem">
          Made the number of strand implementations configurable by defining <code class="computeroutput"><span class="identifier">BOOST_ASIO_STRAND_IMPLEMENTATIONS</span></code> to
          the desired number.
        </li>
<li class="listitem">
          Added support for a new <code class="computeroutput"><span class="identifier">BOOST_ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION</span></code>
          flag which switches the allocation of strand implementations to use a round-robin
          approach rather than hashing.
        </li>
<li class="listitem">
          Fixed potential strand starvation issue that can occur when <code class="computeroutput"><span class="identifier">strand</span><span class="special">.</span><span class="identifier">post</span><span class="special">()</span></code>
          is used.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h49"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_6_0___boost_1_47"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_6_0___boost_1_47">Asio
      1.6.0 / Boost 1.47</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added support for signal handling, using a new class called <code class="computeroutput"><span class="identifier">signal_set</span></code>. Programs may add one or more
          signals to the set, and then perform an <code class="computeroutput"><span class="identifier">async_wait</span><span class="special">()</span></code> operation. The specified handler will
          be called when one of the signals occurs. The same signal number may be
          registered with multiple <code class="computeroutput"><span class="identifier">signal_set</span></code>
          objects, however the signal number must be used only with Asio. Addresses
          <a href="https://svn.boost.org/trac/boost/ticket/2879" target="_top">#2879</a>.
        </li>
<li class="listitem">
          Added handler tracking, a new debugging aid. When enabled by defining
          <code class="computeroutput"><span class="identifier">BOOST_ASIO_ENABLE_HANDLER_TRACKING</span></code>,
          Asio writes debugging output to the standard error stream. The output records
          asynchronous operations and the relationships between their handlers. It
          may be post-processed using the included <code class="literal">handlerviz.pl</code>
          tool to create a visual representation of the handlers (requires GraphViz).
        </li>
<li class="listitem">
          Added support for timeouts on socket iostreams, such as <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">iostream</span></code>.
          A timeout is set by calling <code class="computeroutput"><span class="identifier">expires_at</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">expires_from_now</span><span class="special">()</span></code> to establish a deadline. Any socket operations
          which occur past the deadline will put the iostream into a bad state.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">error</span><span class="special">()</span></code>
          member function to socket iostreams, for retrieving the error code from
          the most recent system call.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">basic_deadline_timer</span><span class="special">::</span><span class="identifier">cancel_one</span><span class="special">()</span></code> function. This function lets you cancel
          a single waiting handler on a timer. Handlers are cancelled in FIFO order.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">transfer_exactly</span><span class="special">()</span></code> completion condition. This can be used
          to send or receive a specified number of bytes even if the total size of
          the buffer (or buffer sequence) is larger.
        </li>
<li class="listitem">
          Added new free functions <code class="computeroutput"><span class="identifier">connect</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">async_connect</span><span class="special">()</span></code>. These operations try each endpoint in
          a list until the socket is successfully connected, and are useful for creating
          TCP clients that work with both IPv4 and IPv6.
        </li>
<li class="listitem">
          Extended the <code class="computeroutput"><span class="identifier">buffer_size</span><span class="special">()</span></code> function so that it works for buffer
          sequences in addition to individual buffers.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">buffer_copy</span><span class="special">()</span></code> function that can be used to copy the
          raw bytes between individual buffers and buffer sequences.
        </li>
<li class="listitem">
          Added new non-throwing overloads of <code class="computeroutput"><span class="identifier">read</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">read_at</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">write</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">write_at</span><span class="special">()</span></code> that do not require a completion condition.
        </li>
<li class="listitem">
          Added friendlier compiler errors for when a completion handler does not
          meet the necessary type requirements. When C++0x is available (currently
          supported for <code class="literal">g++</code> 4.5 or later, and MSVC 10), <code class="computeroutput"><span class="keyword">static_assert</span></code> is also used to generate an
          informative error message. This checking may be disabled by defining <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_HANDLER_TYPE_REQUIREMENTS</span></code>.
        </li>
<li class="listitem">
          Added a new, completely rewritten SSL implementation. The new implementation
          compiles faster, shows substantially improved performance, and supports
          custom memory allocation and handler invocation. It includes new API features
          such as certificate verification callbacks and has improved error reporting.
          The new implementation is source-compatible with the old for most uses.
          However, if necessary, the old implementation may still be used by defining
          <code class="computeroutput"><span class="identifier">BOOST_ASIO_ENABLE_OLD_SSL</span></code>.
          Addresses <a href="https://svn.boost.org/trac/boost/ticket/3702" target="_top">#3702</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/3958" target="_top">#3958</a>.
        </li>
<li class="listitem">
          Changed the separate compilation support such that, to use Asio's SSL capabilities,
          you should also include <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">asio</span><span class="special">/</span><span class="identifier">ssl</span><span class="special">/</span><span class="identifier">impl</span><span class="special">/</span><span class="identifier">src</span><span class="special">.</span><span class="identifier">hpp</span></code>
          in one source file in your program.
        </li>
<li class="listitem">
          Changed the SSL implementation to support build environments where SSL
          v2 is explicitly disabled (<a href="https://svn.boost.org/trac/boost/ticket/5453" target="_top">#5453</a>).
        </li>
<li class="listitem">
          Made the <code class="computeroutput"><span class="identifier">is_loopback</span><span class="special">()</span></code>,
          <code class="computeroutput"><span class="identifier">is_unspecified</span><span class="special">()</span></code>
          and <code class="computeroutput"><span class="identifier">is_multicast</span><span class="special">()</span></code>
          functions consistently available across the <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address</span></code>,
          <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v4</span></code> and <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v6</span></code>
          classes (<a href="https://svn.boost.org/trac/boost/ticket/3939" target="_top">#3939</a>).
        </li>
<li class="listitem">
          Added new <code class="computeroutput"><span class="identifier">non_blocking</span><span class="special">()</span></code> functions for managing the non-blocking
          behaviour of a socket or descriptor. The <code class="computeroutput"><span class="identifier">io_control</span><span class="special">()</span></code> commands named <code class="computeroutput"><span class="identifier">non_blocking_io</span></code>
          are now deprecated in favour of these new functions.
        </li>
<li class="listitem">
          Added new <code class="computeroutput"><span class="identifier">native_non_blocking</span><span class="special">()</span></code> functions for managing the non-blocking
          mode of the underlying socket or descriptor. These functions are intended
          to allow the encapsulation of arbitrary non-blocking system calls as asynchronous
          operations, in a way that is transparent to the user of the socket object.
          The functions have no effect on the behaviour of the synchronous operations
          of the socket or descriptor.
        </li>
<li class="listitem">
          Added the <code class="computeroutput"><span class="identifier">io_control</span><span class="special">()</span></code>
          member function for socket acceptors (<a href="https://svn.boost.org/trac/boost/ticket/3297" target="_top">#3297</a>).
        </li>
<li class="listitem">
          Added a <code class="computeroutput"><span class="identifier">release</span><span class="special">()</span></code>
          member function to posix descriptors. This function releases ownership
          of the underlying native descriptor to the caller. Addresses <a href="https://svn.boost.org/trac/boost/ticket/3900" target="_top">#3900</a>.
        </li>
<li class="listitem">
          Added support for sequenced packet sockets (<code class="computeroutput"><span class="identifier">SOCK_SEQPACKET</span></code>).
        </li>
<li class="listitem">
          Added a new <code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">stopped</span><span class="special">()</span></code> function that can be used to determine
          whether the <code class="computeroutput"><span class="identifier">io_service</span></code>
          has stopped (i.e. a <code class="computeroutput"><span class="identifier">reset</span><span class="special">()</span></code> call is needed prior to any further calls
          to <code class="computeroutput"><span class="identifier">run</span><span class="special">()</span></code>,
          <code class="computeroutput"><span class="identifier">run_one</span><span class="special">()</span></code>,
          <code class="computeroutput"><span class="identifier">poll</span><span class="special">()</span></code>
          or <code class="computeroutput"><span class="identifier">poll_one</span><span class="special">()</span></code>).
        </li>
<li class="listitem">
          For consistency with the C++0x standard library, deprecated the <code class="computeroutput"><span class="identifier">native_type</span></code> typedefs in favour of <code class="computeroutput"><span class="identifier">native_handle_type</span></code>, and the <code class="computeroutput"><span class="identifier">native</span><span class="special">()</span></code>
          member functions in favour of <code class="computeroutput"><span class="identifier">native_handle</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Added support for C++0x move construction and assignment to sockets, serial
          ports, POSIX descriptors and Windows handles.
        </li>
<li class="listitem">
          Reduced the copying of handler function objects.
        </li>
<li class="listitem">
          Added support for C++0x move construction to further reduce (and in some
          cases eliminate) copying of handler objects.
        </li>
<li class="listitem">
          Added support for the <code class="computeroutput"><span class="identifier">fork</span><span class="special">()</span></code> system call. Programs that use <code class="computeroutput"><span class="identifier">fork</span><span class="special">()</span></code>
          must call <code class="computeroutput"><span class="identifier">io_service</span><span class="special">.</span><span class="identifier">notify_fork</span><span class="special">()</span></code>
          at the appropriate times. Two new examples have been added showing how
          to use this feature. Addresses <a href="https://svn.boost.org/trac/boost/ticket/3238" target="_top">#3238</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/4162" target="_top">#4162</a>.
        </li>
<li class="listitem">
          Cleaned up the handling of errors reported by the <code class="computeroutput"><span class="identifier">close</span><span class="special">()</span></code> system call. In particular, assume that
          most operating systems won't have <code class="computeroutput"><span class="identifier">close</span><span class="special">()</span></code> fail with <code class="computeroutput"><span class="identifier">EWOULDBLOCK</span></code>,
          but if it does then set the blocking mode and restart the call. If any
          other error occurs, assume the descriptor is closed. Addresses <a href="https://svn.boost.org/trac/boost/ticket/3307" target="_top">#3307</a>.
        </li>
<li class="listitem">
          Added new <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">buffer</span><span class="special">()</span></code>
          overloads for <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">array</span></code>, when available.
        </li>
<li class="listitem">
          Changed the implementation to use the C++0x standard library templates
          <code class="computeroutput"><span class="identifier">array</span></code>, <code class="computeroutput"><span class="identifier">shared_ptr</span></code>,
          <code class="computeroutput"><span class="identifier">weak_ptr</span></code> and <code class="computeroutput"><span class="identifier">atomic</span></code> when they are available, rather
          than the Boost equivalents.
        </li>
<li class="listitem">
          Use C++0x variadic templates when available, rather than generating function
          overloads using Boost.Preprocessor.
        </li>
<li class="listitem">
          Changed exception reporting to include the function name in exception
          <code class="computeroutput"><span class="identifier">what</span><span class="special">()</span></code>
          messages.
        </li>
<li class="listitem">
          Fixed insufficient initialisers warning with MinGW.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">shutdown_service</span><span class="special">()</span></code> member functions to be private.
        </li>
<li class="listitem">
          Added archetypes for testing socket option functions.
        </li>
<li class="listitem">
          Changed the Boost.Asio examples so that they don't use Boost.Thread's convenience
          header. Use the header file that is specifically for the boost::thread
          class instead.
        </li>
<li class="listitem">
          Removed the dependency on OS-provided macros for the well-known IPv4 and
          IPv6 addresses. This should eliminate annoying "missing braces around
          initializer" warnings (<a href="https://svn.boost.org/trac/boost/ticket/3741" target="_top">#3741</a>).
        </li>
<li class="listitem">
          Reduced the size of <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">basic_endpoint</span><span class="special">&lt;&gt;</span></code> objects (such as <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">endpoint</span></code> and <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span><span class="special">::</span><span class="identifier">endpoint</span></code>).
        </li>
<li class="listitem">
          Changed the reactor backends to assume that any descriptors or sockets
          added using <code class="computeroutput"><span class="identifier">assign</span><span class="special">()</span></code>
          may have been <code class="computeroutput"><span class="identifier">dup</span><span class="special">()</span></code>-ed,
          and so require explicit deregistration from the reactor (<a href="https://svn.boost.org/trac/boost/ticket/4971" target="_top">#4971</a>).
        </li>
<li class="listitem">
          Removed the deprecated member functions named <code class="computeroutput"><span class="identifier">io_service</span><span class="special">()</span></code>. The <code class="computeroutput"><span class="identifier">get_io_service</span><span class="special">()</span></code> member functions should be used instead.
        </li>
<li class="listitem">
          Removed the deprecated typedefs <code class="computeroutput"><span class="identifier">resolver_query</span></code>
          and <code class="computeroutput"><span class="identifier">resolver_iterator</span></code> from
          the <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span></code>, <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span></code>
          and <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">icmp</span></code> classes.
        </li>
<li class="listitem">
          Modified the <code class="computeroutput"><span class="identifier">buffers_iterator</span><span class="special">&lt;&gt;</span></code> and <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">basic_resolver_iterator</span></code>
          classes so that the value_type typedefs are non-const byte types.
        </li>
<li class="listitem">
          Fixed warnings reported by g++'s <code class="literal">-Wshadow</code> compiler option
          (<a href="https://svn.boost.org/trac/boost/ticket/3905" target="_top">#3905</a>).
        </li>
<li class="listitem">
          Added an explicit cast to convert the <code class="computeroutput"><span class="identifier">FIONBIO</span></code>
          constant to int, to suppress a compiler warning on some platforms (<a href="https://svn.boost.org/trac/boost/ticket/5128" target="_top">#5128</a>).
        </li>
<li class="listitem">
          Changed most examples to treat a failure by an accept operation as non-fatal
          (<a href="https://svn.boost.org/trac/boost/ticket/5124" target="_top">#5124</a>).
        </li>
<li class="listitem">
          Fixed an error in the <code class="literal">tick_count_timer</code> example by making
          the duration type signed. Previously, a wait on an already-passed deadline
          would not return for a very long time (<a href="https://svn.boost.org/trac/boost/ticket/5418" target="_top">#5418</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h50"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_9___boost_1_46_1"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_9___boost_1_46_1">Asio
      1.4.9 / Boost 1.46.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          <code class="computeroutput"><span class="identifier">EV_ONESHOT</span></code> seems to cause
          problems on some versions of Mac OS X, with the <code class="computeroutput"><span class="identifier">io_service</span></code>
          destructor getting stuck inside the <code class="computeroutput"><span class="identifier">close</span><span class="special">()</span></code> system call. Changed the kqueue backend
          to use <code class="computeroutput"><span class="identifier">EV_CLEAR</span></code> instead
          (<a href="https://svn.boost.org/trac/boost/ticket/5021" target="_top">#5021</a>).
        </li>
<li class="listitem">
          Fixed compile failures with some versions of <code class="literal">g++</code> due
          to the use of anonymous enums (<a href="https://svn.boost.org/trac/boost/ticket/4883" target="_top">#4883</a>).
        </li>
<li class="listitem">
          Fixed a bug on kqueue-based platforms, where some system calls that repeatedly
          fail with <code class="computeroutput"><span class="identifier">EWOULDBLOCK</span></code> are
          not correctly re-registered with kqueue.
        </li>
<li class="listitem">
          Changed <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span></code> to ensure that its internal
          pointers are updated correctly after the data has been modified using
          <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">streambuf</span></code> member functions.
        </li>
<li class="listitem">
          Fixed a bug that prevented the linger socket option from working on platforms
          other than Windows.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h51"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_8___boost_1_46"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_8___boost_1_46">Asio
      1.4.8 / Boost 1.46</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed an integer overflow problem that occurs when <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">address_v4</span><span class="special">::</span><span class="identifier">broadcast</span><span class="special">()</span></code> is used on 64-bit platforms.
        </li>
<li class="listitem">
          Fixed a problem on older Linux kernels (where epoll is used without timerfd
          support) that prevents timely delivery of deadline_timer handlers, after
          the program has been running for some time (<a href="https://svn.boost.org/trac/boost/ticket/5045" target="_top">#5045</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h52"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_7___boost_1_45"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_7___boost_1_45">Asio
      1.4.7 / Boost 1.45</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Fixed a problem on kqueue-based platforms where a <code class="computeroutput"><span class="identifier">deadline_timer</span></code>
          may never fire if the <code class="computeroutput"><span class="identifier">io_service</span></code>
          is running in a background thread (<a href="https://svn.boost.org/trac/boost/ticket/4568" target="_top">#4568</a>).
        </li>
<li class="listitem">
          Fixed a const-correctness issue that prevented valid uses of <code class="computeroutput"><span class="identifier">has_service</span><span class="special">&lt;&gt;</span></code>
          from compiling (<a href="https://svn.boost.org/trac/boost/ticket/4638" target="_top">#4638</a>).
        </li>
<li class="listitem">
          Fixed MinGW cross-compilation (<a href="https://svn.boost.org/trac/boost/ticket/4491" target="_top">#4491</a>).
        </li>
<li class="listitem">
          Removed dependency on deprecated Boost.System functions (<a href="https://svn.boost.org/trac/boost/ticket/4672" target="_top">#4672</a>).
        </li>
<li class="listitem">
          Ensured <code class="computeroutput"><span class="identifier">close</span><span class="special">()</span></code>/<code class="computeroutput"><span class="identifier">closesocket</span><span class="special">()</span></code>
          failures are correctly propagated (<a href="https://svn.boost.org/trac/boost/ticket/4573" target="_top">#4573</a>).
        </li>
<li class="listitem">
          Added a check for errors returned by <code class="computeroutput"><span class="identifier">InitializeCriticalSectionAndSpinCount</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/4574" target="_top">#4574</a>).
        </li>
<li class="listitem">
          Added support for hardware flow control on QNX (<a href="https://svn.boost.org/trac/boost/ticket/4625" target="_top">#4625</a>).
        </li>
<li class="listitem">
          Always use <code class="computeroutput"><span class="identifier">pselect</span><span class="special">()</span></code>
          on HP-UX, if it is available (<a href="https://svn.boost.org/trac/boost/ticket/4578" target="_top">#4578</a>).
        </li>
<li class="listitem">
          Ensured handler arguments are passed as lvalues (<a href="https://svn.boost.org/trac/boost/ticket/4744" target="_top">#4744</a>).
        </li>
<li class="listitem">
          Fixed Windows build when thread support is disabled (<a href="https://svn.boost.org/trac/boost/ticket/4680" target="_top">#4680</a>).
        </li>
<li class="listitem">
          Fixed a Windows-specific problem where <code class="computeroutput"><span class="identifier">deadline_timer</span></code>
          objects with expiry times set more than 5 minutes in the future may never
          expire (<a href="https://svn.boost.org/trac/boost/ticket/4745" target="_top">#4745</a>).
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput"><span class="identifier">resolver</span></code> backend
          on BSD platforms so that an empty service name resolves to port number
          <code class="computeroutput"><span class="number">0</span></code>, as per the documentation
          (<a href="https://svn.boost.org/trac/boost/ticket/4690" target="_top">#4690</a>).
        </li>
<li class="listitem">
          Fixed read operations so that they do not accept buffer sequences of type
          <code class="computeroutput"><span class="identifier">const_buffers_1</span></code> (<a href="https://svn.boost.org/trac/boost/ticket/4746" target="_top">#4746</a>).
        </li>
<li class="listitem">
          Redefined <code class="computeroutput"><span class="identifier">Protocol</span></code> and
          <code class="computeroutput"><span class="identifier">id</span></code> to avoid clashing with
          Objective-C++ keywords (<a href="https://svn.boost.org/trac/boost/ticket/4191" target="_top">#4191</a>).
        </li>
<li class="listitem">
          Fixed a <code class="computeroutput"><span class="identifier">vector</span></code> reallocation
          performance issue that can occur when there are many active <code class="computeroutput"><span class="identifier">deadline_timer</span></code> objects (<a href="https://svn.boost.org/trac/boost/ticket/4780" target="_top">#4780</a>).
        </li>
<li class="listitem">
          Fixed the kqueue backend so that it compiles on NetBSD (<a href="https://svn.boost.org/trac/boost/ticket/4662" target="_top">#4662</a>).
        </li>
<li class="listitem">
          Fixed the socket <code class="computeroutput"><span class="identifier">io_control</span><span class="special">()</span></code> implementation on 64-bit Mac OS X and
          BSD platforms (<a href="https://svn.boost.org/trac/boost/ticket/4782" target="_top">#4782</a>).
        </li>
<li class="listitem">
          Fixed a Windows-specific problem where failures from <code class="computeroutput"><span class="identifier">accept</span><span class="special">()</span></code> are incorrectly treated as successes
          (<a href="https://svn.boost.org/trac/boost/ticket/4859" target="_top">#4859</a>).
        </li>
<li class="listitem">
          Deprecated the separate compilation header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">asio</span><span class="special">/</span><span class="identifier">impl</span><span class="special">/</span><span class="identifier">src</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">&gt;</span></code>
          in favour of <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">asio</span><span class="special">/</span><span class="identifier">impl</span><span class="special">/</span><span class="identifier">src</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code> (<a href="https://svn.boost.org/trac/boost/ticket/4560" target="_top">#4560</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h53"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_6___boost_1_44"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_6___boost_1_44">Asio
      1.4.6 / Boost 1.44</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Reduced compile times. (Note that some programs may need to add additional
          <code class="computeroutput"><span class="preprocessor">#include</span></code>s, e.g. if the
          program uses <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">array</span></code> but does not explicitly include
          <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">array</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>.)
        </li>
<li class="listitem">
          Reduced the size of generated code.
        </li>
<li class="listitem">
          Refactored <code class="computeroutput"><span class="identifier">deadline_timer</span></code>
          implementation to improve performance.
        </li>
<li class="listitem">
          Improved multiprocessor scalability on Windows by using a dedicated hidden
          thread to wait for timers.
        </li>
<li class="listitem">
          Improved performance of <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">streambuf</span></code>
          with <code class="computeroutput"><span class="identifier">async_read</span><span class="special">()</span></code>
          and <code class="computeroutput"><span class="identifier">async_read_until</span><span class="special">()</span></code>.
          These read operations now use the existing capacity of the <code class="computeroutput"><span class="identifier">streambuf</span></code> when reading, rather than limiting
          the read to 512 bytes.
        </li>
<li class="listitem">
          Added optional separate compilation. To enable, add <code class="computeroutput"><span class="preprocessor">#include</span>
          <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">asio</span><span class="special">/</span><span class="identifier">impl</span><span class="special">/</span><span class="identifier">src</span><span class="special">.</span><span class="identifier">cpp</span><span class="special">&gt;</span></code> to one source file in a program, then
          build the program with <code class="computeroutput"><span class="identifier">BOOST_ASIO_SEPARATE_COMPILATION</span></code>
          defined in the project/compiler settings. Alternatively, <code class="computeroutput"><span class="identifier">BOOST_ASIO_DYN_LINK</span></code> may be defined to
          build a separately-compiled Asio as part of a shared library.
        </li>
<li class="listitem">
          Added new macro <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_FENCED_BLOCK</span></code>
          to permit the disabling of memory fences around completion handlers, even
          if thread support is enabled.
        </li>
<li class="listitem">
          Reworked timeout examples to better illustrate typical use cases.
        </li>
<li class="listitem">
          Ensured that handler arguments are passed as <code class="computeroutput"><span class="keyword">const</span></code>
          types.
        </li>
<li class="listitem">
          Fixed incorrect parameter order in <code class="computeroutput"><span class="identifier">null_buffers</span></code>
          variant of <code class="computeroutput"><span class="identifier">async_send_to</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/4170" target="_top">#4170</a>).
        </li>
<li class="listitem">
          Ensured <code class="computeroutput"><span class="keyword">unsigned</span> <span class="keyword">char</span></code>
          is used with <code class="computeroutput"><span class="identifier">isdigit</span></code> in
          <code class="computeroutput"><span class="identifier">getaddrinfo</span></code> emulation (<a href="https://svn.boost.org/trac/boost/ticket/4201" target="_top">#4201</a>).
        </li>
<li class="listitem">
          Fixed handling of very small but non-zero timeouts (<a href="https://svn.boost.org/trac/boost/ticket/4205" target="_top">#4205</a>).
        </li>
<li class="listitem">
          Fixed crash that occurred when an empty buffer sequence was passed to a
          composed read or write operation.
        </li>
<li class="listitem">
          Added missing <code class="computeroutput"><span class="keyword">operator</span><span class="special">+</span></code>
          overload in <code class="computeroutput"><span class="identifier">buffers_iterator</span></code>
          (<a href="https://svn.boost.org/trac/boost/ticket/4382" target="_top">#4382</a>).
        </li>
<li class="listitem">
          Implemented cancellation of <code class="computeroutput"><span class="identifier">null_buffers</span></code>
          operations on Windows.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h54"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_5___boost_1_43"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_5___boost_1_43">Asio
      1.4.5 / Boost 1.43</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Improved performance.
        </li>
<li class="listitem">
          Reduced compile times.
        </li>
<li class="listitem">
          Reduced the size of generated code.
        </li>
<li class="listitem">
          Extended the guarantee that background threads don't call user code to
          all asynchronous operations (<a href="https://svn.boost.org/trac/boost/ticket/3923" target="_top">#3923</a>).
        </li>
<li class="listitem">
          Changed to use edge-triggered epoll on Linux.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput"><span class="identifier">timerfd</span></code>
          for dispatching timers on Linux, when available.
        </li>
<li class="listitem">
          Changed to use one-shot notifications with kqueue on Mac OS X and BSD platforms.
        </li>
<li class="listitem">
          Added a bitmask type <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">resolver_query_base</span><span class="special">::</span><span class="identifier">flags</span></code>
          as per the TR2 proposal. This type prevents implicit conversion from <code class="computeroutput"><span class="keyword">int</span></code> to <code class="computeroutput"><span class="identifier">flags</span></code>,
          allowing the compiler to catch cases where users incorrectly pass a numeric
          port number as the service name.
        </li>
<li class="listitem">
          Added <code class="computeroutput"><span class="preprocessor">#define</span> <span class="identifier">NOMINMAX</span></code>
          for all Windows compilers. Users can define <code class="computeroutput"><span class="identifier">BOOST_ASIO_NO_NOMINMAX</span></code>
          to suppress this definition (<a href="https://svn.boost.org/trac/boost/ticket/3901" target="_top">#3901</a>).
        </li>
<li class="listitem">
          Fixed a bug where 0-byte asynchronous reads were incorrectly passing an
          <code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">eof</span></code> result to the completion handler
          (<a href="https://svn.boost.org/trac/boost/ticket/4023" target="_top">#4023</a>).
        </li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">io_control</span><span class="special">()</span></code> member functions to always call <code class="computeroutput"><span class="identifier">ioctl</span></code> on the underlying descriptor when
          modifying blocking mode (<a href="https://svn.boost.org/trac/boost/ticket/3307" target="_top">#3307</a>).
        </li>
<li class="listitem">
          Changed the resolver implementation to longer require the typedefs <code class="computeroutput"><span class="identifier">InternetProtocol</span><span class="special">::</span><span class="identifier">resolver_query</span></code> and <code class="computeroutput"><span class="identifier">InternetProtocol</span><span class="special">::</span><span class="identifier">resolver_iterator</span></code>,
          as neither typedef is part of the documented <code class="computeroutput"><span class="identifier">InternetProtocol</span></code>
          requirements. The corresponding typedefs in the <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span></code>,
          <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">udp</span></code> and <code class="computeroutput"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">icmp</span></code>
          classes have been deprecated.
        </li>
<li class="listitem">
          Fixed out-of-band handling for reactors not based on <code class="computeroutput"><span class="identifier">select</span><span class="special">()</span></code>.
        </li>
<li class="listitem">
          Added new <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_THREADS</span></code>
          macro that allows Asio's threading support to be independently disabled.
        </li>
<li class="listitem">
          Minor documentation improvements.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h55"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_4___boost_1_42"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_4___boost_1_42">Asio
      1.4.4 / Boost 1.42</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added a new HTTP Server 4 example illustrating the use of stackless coroutines
          with Asio.
        </li>
<li class="listitem">
          Changed handler allocation and invocation to use <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">addressof</span></code>
          to get the address of handler objects, rather than applying <code class="computeroutput"><span class="keyword">operator</span><span class="special">&amp;</span></code>
          directly (<a href="https://svn.boost.org/trac/boost/ticket/2977" target="_top">#2977</a>).
        </li>
<li class="listitem">
          Restricted MSVC buffer debugging workaround to 2008, as it causes a crash
          with 2010 beta 2 (<a href="https://svn.boost.org/trac/boost/ticket/3796" target="_top">#3796</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/3822" target="_top">#3822</a>).
        </li>
<li class="listitem">
          Fixed a problem with the lifetime of handler memory, where Windows needs
          the <code class="computeroutput"><span class="identifier">OVERLAPPED</span></code> structure
          to be valid until both the initiating function call has returned and the
          completion packet has been delivered.
        </li>
<li class="listitem">
          Don't block signals while performing system calls, but instead restart
          the calls if they are interrupted.
        </li>
<li class="listitem">
          Documented the guarantee made by strand objects with respect to order of
          handler invocation.
        </li>
<li class="listitem">
          Changed strands to use a pool of implementations, to make copying of strands
          cheaper.
        </li>
<li class="listitem">
          Ensured that kqueue support is enabled for BSD platforms (<a href="https://svn.boost.org/trac/boost/ticket/3626" target="_top">#3626</a>).
        </li>
<li class="listitem">
          Added a <code class="computeroutput"><span class="identifier">boost_</span></code> prefix to
          the <code class="computeroutput"><span class="keyword">extern</span> <span class="string">"C"</span></code>
          thread entry point function (<a href="https://svn.boost.org/trac/boost/ticket/3809" target="_top">#3809</a>).
        </li>
<li class="listitem">
          In <code class="computeroutput"><span class="identifier">getaddrinfo</span></code> emulation,
          only check the socket type (<code class="computeroutput"><span class="identifier">SOCK_STREAM</span></code>
          or <code class="computeroutput"><span class="identifier">SOCK_DGRAM</span></code>) if a service
          name has been specified. This should allow the emulation to work with raw
          sockets.
        </li>
<li class="listitem">
          Added a workaround for some broken Windows firewalls that make a socket
          appear bound to 0.0.0.0 when it is in fact bound to 127.0.0.1.
        </li>
<li class="listitem">
          Applied a fix for reported excessive CPU usage under Solaris (<a href="https://svn.boost.org/trac/boost/ticket/3670" target="_top">#3670</a>).
        </li>
<li class="listitem">
          Added some support for platforms that use older compilers such as g++ 2.95
          (<a href="https://svn.boost.org/trac/boost/ticket/3743" target="_top">#3743</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h56"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_3___boost_1_40"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_3___boost_1_40">Asio
      1.4.3 / Boost 1.40</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added a new ping example to illustrate the use of ICMP sockets.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput"><span class="identifier">buffered</span><span class="special">*</span><span class="identifier">_stream</span><span class="special">&lt;&gt;</span></code>
          templates to treat 0-byte reads and writes as no-ops, to comply with the
          documented type requirements for <code class="computeroutput"><span class="identifier">SyncReadStream</span></code>,
          <code class="computeroutput"><span class="identifier">AsyncReadStream</span></code>, <code class="computeroutput"><span class="identifier">SyncWriteStream</span></code> and <code class="computeroutput"><span class="identifier">AsyncWriteStream</span></code>.
        </li>
<li class="listitem">
          Changed some instances of the <code class="computeroutput"><span class="keyword">throw</span></code>
          keyword to <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">throw_exception</span><span class="special">()</span></code>
          to allow Asio to be used when exception support is disabled. Note that
          the SSL wrappers still require exception support (<a href="https://svn.boost.org/trac/boost/ticket/2754" target="_top">#2754</a>).
        </li>
<li class="listitem">
          Made Asio compatible with the OpenSSL 1.0 beta (<a href="https://svn.boost.org/trac/boost/ticket/3256" target="_top">#3256</a>).
        </li>
<li class="listitem">
          Eliminated a redundant system call in the Solaris <code class="literal">/dev/poll</code>
          backend.
        </li>
<li class="listitem">
          Fixed a bug in resizing of the bucket array in the internal hash maps (<a href="https://svn.boost.org/trac/boost/ticket/3095" target="_top">#3095</a>).
        </li>
<li class="listitem">
          Ensured correct propagation of the error code when a synchronous accept
          fails (<a href="https://svn.boost.org/trac/boost/ticket/3216" target="_top">#3216</a>).
        </li>
<li class="listitem">
          Ensured correct propagation of the error code when a synchronous read or
          write on a Windows HANDLE fails.
        </li>
<li class="listitem">
          Fixed failures reported when <code class="computeroutput"><span class="identifier">_GLIBCXX_DEBUG</span></code>
          is defined (<a href="https://svn.boost.org/trac/boost/ticket/3098" target="_top">#3098</a>).
        </li>
<li class="listitem">
          Fixed custom memory allocation support for timers (<a href="https://svn.boost.org/trac/boost/ticket/3107" target="_top">#3107</a>).
        </li>
<li class="listitem">
          Tidied up various warnings reported by g++ (<a href="https://svn.boost.org/trac/boost/ticket/1341" target="_top">#1341</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/2618" target="_top">#2618</a>).
        </li>
<li class="listitem">
          Various documentation improvements, including more obvious hyperlinks to
          function overloads, header file information, examples for the handler type
          requirements, and adding enum values to the index (<a href="https://svn.boost.org/trac/boost/ticket/3157" target="_top">#3157</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/2620" target="_top">#2620</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h57"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_2___boost_1_39"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_2___boost_1_39">Asio
      1.4.2 / Boost 1.39</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Implement automatic resizing of the bucket array in the internal hash maps.
          This is to improve performance for very large numbers of asynchronous operations
          and also to reduce memory usage for very small numbers. A new macro <code class="computeroutput"><span class="identifier">BOOST_ASIO_HASH_MAP_BUCKETS</span></code> may be used
          to tweak the sizes used for the bucket arrays. (N.B. this feature introduced
          a bug which was fixed in Asio 1.4.3 / Boost 1.40.)
        </li>
<li class="listitem">
          Add performance optimisation for the Windows IOCP backend for when no timers
          are used.
        </li>
<li class="listitem">
          Prevent locale settings from affecting formatting of TCP and UDP endpoints
          (<a href="https://svn.boost.org/trac/boost/ticket/2682" target="_top">#2682</a>).
        </li>
<li class="listitem">
          Fix a memory leak that occurred when an asynchronous SSL operation's completion
          handler threw an exception (<a href="https://svn.boost.org/trac/boost/ticket/2910" target="_top">#2910</a>).
        </li>
<li class="listitem">
          Fix the implementation of <code class="computeroutput"><span class="identifier">io_control</span><span class="special">()</span></code> so that it adheres to the documented
          type requirements for IoControlCommand (<a href="https://svn.boost.org/trac/boost/ticket/2820" target="_top">#2820</a>).
        </li>
<li class="listitem">
          Fix incompatibility between Asio and ncurses.h (<a href="https://svn.boost.org/trac/boost/ticket/2156" target="_top">#2156</a>).
        </li>
<li class="listitem">
          On Windows, specifically handle the case when an overlapped <code class="computeroutput"><span class="identifier">ReadFile</span></code> call fails with <code class="computeroutput"><span class="identifier">ERROR_MORE_DATA</span></code>. This enables a hack
          where a <code class="computeroutput"><span class="identifier">windows</span><span class="special">::</span><span class="identifier">stream_handle</span></code> can be used with a message-oriented
          named pipe (<a href="https://svn.boost.org/trac/boost/ticket/2936" target="_top">#2936</a>).
        </li>
<li class="listitem">
          Fix system call wrappers to always clear the error on success, as POSIX
          allows successful system calls to modify errno (<a href="https://svn.boost.org/trac/boost/ticket/2953" target="_top">#2953</a>).
        </li>
<li class="listitem">
          Don't include termios.h if <code class="computeroutput"><span class="identifier">BOOST_ASIO_DISABLE_SERIAL_PORT</span></code>
          is defined (<a href="https://svn.boost.org/trac/boost/ticket/2917" target="_top">#2917</a>).
        </li>
<li class="listitem">
          Cleaned up some more MSVC level 4 warnings (<a href="https://svn.boost.org/trac/boost/ticket/2828" target="_top">#2828</a>).
        </li>
<li class="listitem">
          Various documentation fixes (<a href="https://svn.boost.org/trac/boost/ticket/2871" target="_top">#2871</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h58"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_1___boost_1_38"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_1___boost_1_38">Asio
      1.4.1 / Boost 1.38</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Improved compatibility with some Windows firewall software.
        </li>
<li class="listitem">
          Ensured arguments to <code class="computeroutput"><span class="identifier">windows</span><span class="special">::</span><span class="identifier">overlapped_ptr</span><span class="special">::</span><span class="identifier">complete</span><span class="special">()</span></code> are correctly passed to the completion
          handler (<a href="https://svn.boost.org/trac/boost/ticket/2614" target="_top">#2614</a>).
        </li>
<li class="listitem">
          Fixed a link problem and multicast failure on QNX (<a href="https://svn.boost.org/trac/boost/ticket/2504" target="_top">#2504</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/2530" target="_top">#2530</a>).
        </li>
<li class="listitem">
          Fixed a compile error in SSL support on MinGW / g++ 3.4.5.
        </li>
<li class="listitem">
          Drop back to using a pipe for notification if eventfd is not available
          at runtime on Linux (<a href="https://svn.boost.org/trac/boost/ticket/2683" target="_top">#2683</a>).
        </li>
<li class="listitem">
          Various minor bug and documentation fixes (<a href="https://svn.boost.org/trac/boost/ticket/2534" target="_top">#2534</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/2541" target="_top">#2541</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/2607" target="_top">#2607</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/2617" target="_top">#2617</a>,
          <a href="https://svn.boost.org/trac/boost/ticket/2619" target="_top">#2619</a>).
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h59"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_4_0___boost_1_37"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_4_0___boost_1_37">Asio
      1.4.0 / Boost 1.37</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Enhanced CompletionCondition concept with the signature <code class="computeroutput"><span class="identifier">size_t</span>
          <span class="identifier">CompletionCondition</span><span class="special">(</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">total</span><span class="special">)</span></code>,
          where the return value indicates the maximum number of bytes to be transferred
          on the next read or write operation. (The old CompletionCondition signature
          is still supported for backwards compatibility).
        </li>
<li class="listitem">
          New windows::overlapped_ptr class to allow arbitrary overlapped I/O functions
          (such as TransmitFile) to be used with Asio.
        </li>
<li class="listitem">
          On recent versions of Linux, an eventfd descriptor is now used (rather
          than a pipe) to interrupt a blocked select/epoll reactor.
        </li>
<li class="listitem">
          Added const overloads of lowest_layer().
        </li>
<li class="listitem">
          Synchronous read, write, accept and connect operations are now thread safe
          (meaning that it is now permitted to perform concurrent synchronous operations
          on an individual socket, if supported by the OS).
        </li>
<li class="listitem">
          Reactor-based io_service implementations now use lazy initialisation to
          reduce the memory usage of an io_service object used only as a message
          queue.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h60"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_2_0___boost_1_36"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_2_0___boost_1_36">Asio
      1.2.0 / Boost 1.36</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
          Added support for serial ports.
        </li>
<li class="listitem">
          Added support for UNIX domain sockets.
        </li>
<li class="listitem">
          Added support for raw sockets and ICMP.
        </li>
<li class="listitem">
          Added wrappers for POSIX stream-oriented file descriptors (excluding regular
          files).
        </li>
<li class="listitem">
          Added wrappers for Windows stream-oriented <code class="computeroutput"><span class="identifier">HANDLE</span></code>s
          such as named pipes (requires <code class="computeroutput"><span class="identifier">HANDLE</span></code>s
          that work with I/O completion ports).
        </li>
<li class="listitem">
          Added wrappers for Windows random-access <code class="computeroutput"><span class="identifier">HANDLE</span></code>s
          such as files (requires <code class="computeroutput"><span class="identifier">HANDLE</span></code>s
          that work with I/O completion ports).
        </li>
<li class="listitem">
          Added support for reactor-style operations (i.e. they report readiness
          but perform no I/O) using a new <code class="computeroutput"><span class="identifier">null_buffers</span></code>
          type.
        </li>
<li class="listitem">
          Added an iterator type for bytewise traversal of buffer sequences.
        </li>
<li class="listitem">
          Added new <code class="computeroutput"><span class="identifier">read_until</span><span class="special">()</span></code>
          and <code class="computeroutput"><span class="identifier">async_read_until</span><span class="special">()</span></code>
          overloads that take a user-defined function object for locating message
          boundaries.
        </li>
<li class="listitem">
          Added an experimental two-lock queue (enabled by defining <code class="computeroutput"><span class="identifier">BOOST_ASIO_ENABLE_TWO_LOCK_QUEUE</span></code>) that
          may provide better <code class="computeroutput"><span class="identifier">io_service</span></code>
          scalability across many processors.
        </li>
<li class="listitem">
          Various fixes, performance improvements, and more complete coverage of
          the custom memory allocation support.
        </li>
</ul></div>
<h4>
<a name="boost_asio.history.h61"></a>
      <span class="phrase"><a name="boost_asio.history.asio_1_0_0___boost_1_35"></a></span><a class="link" href="history.html#boost_asio.history.asio_1_0_0___boost_1_35">Asio
      1.0.0 / Boost 1.35</a>
    </h4>
<p>
      First release of Asio as part of Boost.
    </p>
</div>
<div class="copyright-footer">Copyright © 2003-2025 Christopher M.
      Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div>
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